Method and apparatus for chrominance quantization parameters signalling

ABSTRACT

A method for inverse quantization of a current block of a picture, the method comprising: receiving a bitstream; obtaining a joint chrominance component residual, JCCR, control flag from the bitstream; obtaining a chrominance mapping information from the bitstream based on the JCCR control flag; obtaining at least one chrominance quantization parameter, QP, offset from the bitstream based on the JCCR control flag; obtaining a QP value for the current chrominance block based on the obtained chrominance mapping information and the at least one obtained chrominance QP offset; performing inverse quantization on the current chrominance block by using the obtained QP value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of International ApplicationNo. PCT/RU2020/050237, filed on Sep. 23, 2020, which claims priority ofinternational patent Application No. PCT/RU2019/000664 filed on Sep. 23,2019. The disclosures of the aforementioned applications are herebyincorporated by reference in their entireties.

TECHNICAL FIELD

Embodiments of the present application (disclosure) generally relate tothe field of picture processing and more particularly to Method andapparatus for Chrominance quantization parameters signaling.

BACKGROUND

Video coding (video encoding and decoding) is used in a wide range ofdigital video applications, for example broadcast digital TV, videotransmission over internet and mobile networks, real-time conversationalapplications such as video chat, video conferencing, DVD and Blu-raydiscs, video content acquisition and editing systems, and camcorders ofsecurity applications.

The amount of video data needed to depict even a relatively short videocan be substantial, which may result in difficulties when the data is tobe streamed or otherwise communicated across a communications networkwith limited bandwidth capacity. Thus, video data is generallycompressed before being communicated across modern daytelecommunications networks. The size of a video could also be an issuewhen the video is stored on a storage device because memory resourcesmay be limited. Video compression devices often use software and/orhardware at the source to code the video data prior to transmission orstorage, thereby decreasing the quantity of data needed to representdigital video images. The compressed data is then received at thedestination by a video decompression device that decodes the video data.With limited network resources and ever-increasing demands of highervideo quality, improved compression and decompression techniques thatimprove compression ratio with little to no sacrifice in picture qualityare desirable.

SUMMARY

Embodiments of the present application provide apparatuses and methodsfor encoding and decoding according to the independent claims.

The foregoing and other objects are achieved by the subject matter ofthe independent claims. Further implementation forms are apparent fromthe dependent claims, the description and the figures.

An embodiment of the present disclosure provides:

A method for inverse quantization of a current block of a picture,wherein the method is performed by a decoder, and the method comprising:

receiving a bitstream;

obtaining a joint chrominance component residual, JCCR, control flagfrom the bitstream;

obtaining a chrominance mapping information from the bitstream based onthe JCCR control flag;

obtaining at least one chrominance quantization parameter, QP, offsetfrom the bitstream based on the JCCR control flag;

obtaining a QP value for the current chrominance block based on theobtained chrominance mapping information and the at least one obtainedchrominance QP offset;

performing inverse quantization on the current chrominance block byusing the determined QP value.

Here, a signalling of PPS and Slice header QP offsets for chrominancecomponent for JCCR mode; and a signalling of sequence parameter set(SPS) chrominance mapping information for JCCR coding mode is performed.

Depending on a SPS JCCR control flag, signalling/decoding of a jointchrominance component residual offset will be performed. Due to theconditioned signaling of the joint chrominance component residualoffset, less information need to be signalled and thus can saveresource.

In an embodiment, the bitstream may comprise an SPS level syntax, andthe JCCR control flag may be obtained from the SPS level syntax.

In an embodiment, the JCCR control flag may be thesps_joint_cbcr_enabled_flag.

Here, sps_joint_cbcr_enabled_flag specifies whether the joint coding ofchroma residuals is enabled or not. Where sps_joint_cbcr_enabled_flagequal to 1 specifies that the joint coding of chroma residuals isenabled for a coded layer video sequence, CLVS,sps_joint_cbcr_enabled_flag equal to 0 specifies that the joint codingof chroma residuals is disabled for the code layer video sequence;wherein when not present, the value of sps_joint_cbcr_enabled_flag isinferred to be equal to 0.

In an embodiment, if the value of the sps_joint_cbcr_enabled_flag is 1,the at least one obtained chrominance QP offset may be specified byslice_joint_cbcr_qp_offset. Where slice_joint_cbcr_qp_offset is a syntaxelement can be presented in a slice header syntax and specifies adifference to be added to the value of pps_joint_cbcr_qp_offset_valuewhen determining the value of the Qp′_(CbCr). The value ofslice_joint_cbcr_qp_offset shall be in the range of −12 to +12,inclusive. When slice_joint_cbcr_qp_offset is not present, it isinferred to be equal to 0. The value ofpps_joint_cbcr_qp_offset_value+slice_joint_cbcr_qp_offset shall be inthe range of −12 to +12, inclusive.

Here, the flag slice_joint_cbcr_qp_offset may also be denotedsh_joint_cbcr_qp_offset.

In an embodiment, the chrominance mapping information may comprisedelta_qp_in_val_minus1[i][j] and delta_qp_out_val[i][j], and thechrominance mapping information may be obtained from an SPS level syntaxcomprised in the bitstream.

Here, sps_delta_qp_in_val_minus1[i][j] specifies a delta value used toderive an input coordinate of an j-th pivot point of an i-th chroma QPmapping table; wherein when not present, the value ofsps_delta_qp_in_val_minus1[0][j] is inferred to be equal to 0; where i,j are integer values. Where delta_qp_out_val[i][j] specifies a deltavalue used to derive the output coordinate of the j-th pivot point ofthe i-th chroma QP mapping table. When delta_qp_out_val[0][j] is notpresent in the bitstream, the value of delta_qp_out_val[0][j] isinferred to be equal to 0. Where delta_qp_out_val may also be denotedsps_delta_qp_diff_val.

In an embodiment, the SPS level syntax may comprise the followingstructure:

seq_parameter_set_rbsp( ) { Descriptor ...  if( ChromaArrayType != 0 ) {  same_qp_table_for_chroma u(1)   for( i = 0; i <same_qp_table_for_chroma ? 1 : sps_   joint_cbcr_enabled_flag ? 3 : 2;i++ ) {    num_points_in_qp_table_minus1[ i ] ue(v)    for( j = 0; j <=num_points_in_qp_table_minus1[ i ];    j++ ) {    delta_qp_in_val_minus1[ i ][ j ] ue(v) ... ue(v)    }   }  } ... }

Thus, a signalling of PPS and Slice header QP offsets for chrominancecomponent for JCCR mode; and a signalling of SPS chrominance mappinginformation for JCCR coding mode may be performed depending on SPS JCCRcontrol flag according to the above tables. For example, the sps JCCRcontrol flag is the sps_joint_cbcr_enabled_flag signalled in SPS levelsyntax, e.g., the seq_parameter_set_rbsp syntax. In particular, it maybe seen that, the value of the index “i” is determined based on thevalue of sps_joint_cbcr_enabled_flag, thus redundant signalling of JCCRsyntax elements can be avoided when JCCR tool is disabled. It can beseen that, the signalling/decoding of pps_joint_cbcr_qp_offset isdepending on sps_joint_cbcr_enabled_flag, that is, only when the valueof sps_joint_cbcr_enabled_flag is true (e.g., 1), thepps_joint_cbcr_qp_offset will be signalled or can be decoded. Due to theconditioned signaling of pps_joint_cbcr_qp_offset, less information needto be signalled and thus can save resource.

Here, seq_parameter_set_rbsp refers to the sequence parameter set RawByte Sequence Payload, RBSP, syntax; wheresps_num_points_in_qp_table_minus1[i] plus 1 specifies the number ofpoints used to describe the i-th chroma QP mapping table; wherein thevalue of sps_num_points_in_qp_table_minus1[i] is in the range of 0 to36; wherein when not present, the value ofsps_num_points_in_qp_table_minus1[0] is inferred to be equal to 0.

In an embodiment, the obtaining the at least one chrominance QP offsetfrom the bitstream based on the JCCR control flag may compriseobtaining, based on the JCCR control flag, the at least one chrominanceQP offset from a picture parameter set, PPS, level syntax of thebitstream.

In an embodiment, the PPS level syntax may comprise the followingstructure:

pic_parameter_set_rbsp( ) { Descriptor ...  pps_cb_qp_offset se(v) pps_cr_qp_offset se(v)  if( sps_joint_cbcr_enabled_flag )  pps_joint_cbcr_qp_offset se(v)  cu_chroma_qp_offset_enabled_flag u(1) if( pps_cu_chroma_qp_offset_list_enabled_flag ) {  cu_chroma_qp_offset_subdiv ue(v)   chroma_qp_offset_list_len_minus1ue(v)   for( i = 0; i <= chroma_qp_offset_list_len_minus1;   i++ ) {   cb_qp_offset_list[ i ] se(v)    cr_qp_offset_list[ i ] se(v)    if(sps_joint_cbcr_enabled_flag )     joint_cbcr_qp_offset_list[ i ] se(v)  }  } ... }

Here, pic_parameter_set_rbsp refers to the Picture parameter set RBSPsyntax; where pps_cb_qp_offset and pps_cr_qp_offset specify the offsetsto the luma quantization parameter Qp′_(Y) used for deriving Qp′_(Cb)and Qp′_(Cr), respectively; wherein the values of pps_cb_qp_offset andpps_cr_qp_offset are in the range of −12 to +12, inclusive; wherein whensps_chroma_format_idc is equal to 0, pps_cb_qp_offset andpps_cr_qp_offset are not used in the decoding process decoders shallignore their value; wherein when not present, the values ofpps_cb_qp_offset and pps_cr_qp_offset are inferred to be equal to 0;wherein sps_joint_cbcr_enabled_flag equal to 1 specifies that the jointcoding of chroma residuals is enabled for a coded layer video sequence,CLVS, where sps_joint_cbcr_enabled_flag equal to 0 specifies that thejoint coding of chroma residuals is disabled for the CLVS; wherein whennot present, the value of sps_joint_cbcr_enabled_flag is inferred to beequal to 0. wherein pps_joint_cbcr_qp_offset_value specifies the offsetto the luma quantization parameter Qp′_(Y) used for deriving Qp′_(CbCr);wherein the value of pps_joint_cbcr_qp_offset_value is in the range of−12 to +12, inclusive.

An embodiment of the present disclosure further provides a method forinverse quantization of a current block of a picture, wherein the methodis performed by a decoder, and the method comprising:

receiving a bitstream, wherein the bitstream comprises a Slice Headersyntax and a PPS syntax;

obtaining syntax elements from the PPS syntax, wherein the obtainedsyntax elements comprise at least one chrominance quantizationparameter, QP, offsets;

obtaining chrominance QP offset information from the Slice Header,wherein the QP offset information is obtained independently of any PPSsyntax elements in the PPS syntax;

determining a QP value for the current chrominance block depending onthe at least one chrominance QP offset obtained from the PPS syntax andthe chrominance QP offset information obtained from the Slice Headersyntax;

performing inverse quantization on the current chrominance block byusing the determined QP value.

Thus, a signalling of PPS and Slice header QP offsets for chrominancecomponent is performed independently of each other's according to thetable shown above. Instead, previously, a flagpps_slice_chroma_qp_offsets_present_flag is signalled in PPS levelsyntax, which control whether there is any further offsets signaling inslice header, that is, at the decoder side, the decoder need to checkthe value of the pps_slice_chroma_qp_offsets_present_flag to determinewhether there is any further offsets signaled in the slice header.Comparing to the previous method, now, in the method described above,the flag pps_slice_chroma_qp_offsets_present_flag is not signaled anymore. In other words, there are offsets always signaled in the sliceheader, therefore, the decoder knows that there are further offsetssignaled in the slice header without check the value of thepps_slice_chroma_qp_offsets_present_flag, in other words, the PPS levelsyntax and the slice header syntax will always both include offsets.Thus, the decoding/signalling of chrominance QP offsets in slice headerbecomes simpler.

In an embodiment, the at least one chrominance QP offset obtained fromthe PPS syntax may comprise: pps_cb_qp_offset, pps_cr_qp_offset,pps_joint_cbcr_qp_offset, and cu_chroma_qp_offset_enabled_flag.

In an embodiment, if the value of the cu_chroma_qp_offset_enabled_flagis 1, the at least one chrominance QP offset obtained from the PPSsyntax further may comprise: cu_chroma_qp_offset_subdiv,chroma_qp_offset_list_len_minus1, cb_qp_offset_list[i],cr_qp_offset_list[i] and joint_cbcr_qp_offset_list[i], wherein0≤i≤chroma_qp_offset_list_len_minus1 and i is a integer.

In an embodiment, the chrominance QP offset information obtained fromthe Slice Header syntax may comprise: slice_cb_qp_offset andslice_cr_qp_offset.

In an embodiment, if the value of sps_joint_cbcr_enabled_flag comprisedin the bitstream is 1, the chrominance QP offset information obtainedfrom the Slice Header syntax may further comprise:slice_joint_cbcr_qp_offset.

In an embodiment, the PPS syntax may comprise the following structure:

pic_parameter_set_rbsp( ) { Descriptor ...  pps_cb_qp_offset se(v) pps_cr_qp_offset se(v)  pps_joint_cbcr_qp_offset se(v) cu_chroma_qp_offset_enabled_flag u(1)  if(cu_chroma_qp_offset_enabled_flag ) {   cu_chroma_qp_offset_subdiv ue(v)  chroma_qp_offset_list_len_minus1 ue(v)   for( i = 0; i <=chroma_qp_offset_list_len_minus1;   i++ ) {    cb_qp_offset_list[ i ]se(v)    cr_qp_offset_list[ i ] se(v)    joint_cbcr_qp_offset_list[ i ]se(v)   }  } ... }

In an embodiment, the slice header syntax may comprise the followingstructure:

slice_header( ) { Descriptor ...  slice_cb_qp_offset se(v) slice_cr_qp_offset se(v)  if( sps_joint_cbcr_enabled_flag )  slice_joint_cbcr_qp_offset se(v) ... }

In an embodiment, the flag pps_slice_chroma_qp_offsets_present_flag maybe omitted in the PPS syntax; or

the Slice Header and the PPS syntax may always comprise elements relatedto the at least one chrominance QP offset.

The present disclosure further provides, in an embodiment, a method forinverse quantization of a current block of a picture, wherein the methodis performed by an encoder, the method comprising:

encoding a joint chrominance component residual, JCCR, control flag intoa bitstream;

encoding a chrominance mapping information into the bitstream based onthe JCCR control flag;

encoding at least one chrominance quantization parameter, (QP, offsetinto the bitstream based on the JCCR control flag;

providing the bitstream.

In an embodiment, the bitstream may comprise an SPS level syntax, andthe JCCR control flag is encoded into the SPS level syntax.

In an embodiment, the JCCR control flag may be thesps_joint_cbcr_enabled_flag.

In an embodiment, if the value of the sps_joint_cbcr_enabled_flag is 1,the at least one encoded chrominance QP offset may be specified byslice_joint_cbcr_qp_offset.

In an embodiment, the chrominance mapping information may comprisedelta_qp_in_val_minus1[i][j] and delta_qp_out_val[i][j], and thechrominance mapping information may be encoded into an SPS level syntaxcomprised in the bitstream.

In an embodiment, the SPS level syntax may comprise the followingstructure:

seq_parameter_set_rbsp( ) { Descriptor ...  if( ChromaArrayType != 0 ) {  same_qp_table_for_chroma u(1)   for( i = 0; i <same_qp_table_for_chroma ? 1 : sps_joint_   cbcr_enabled_flag ? 3 : 2;i++ ) {    num_points_in_qp_table_minus1[ i ] ue(v)    for( j = 0; j <=num_points_in_qp_table_minus1[ i ];    j++ ) {    delta_qp_in_val_minus1[ i ][ j ] ue(v) ... ue(v)    }   }  } ... }

Where same_qp_table_for_chroma indicates how many chroma QP mappingtables have been signaled. When same_qp_table_for_chroma equal to 1specifies that only one chroma QP mapping table is signalled and thistable applies to Cb and Cr residuals and additionally to joint Cb-Crresiduals when sps_joint_cbcr_enabled_flag is equal to 1.same_qp_table_for_chroma equal to 0 specifies that chroma QP mappingtables, two for Cb and Cr, and one additional for joint Cb-Cr whensps_joint_cbcr_enabled_flag is equal to 1, are signalled in the SPS.When same_qp_table_for_chroma is not present in the bitstream, the valueof same_qp_table_for_chroma is inferred to be equal to 1.

Where num_points_in_qp_table_minus1[i] plus 1 specifies the number ofpoints used to describe the i-th chroma QP mapping table. The value ofnum_points_in_qp_table_minus1[i] shall be in the range of 0 to63+QpBdOffset, inclusive. When num_points_in_qp_table_minus1[0] is notpresent in the bitstream, the value of num_points_in_qp_table_minus1[0]is inferred to be equal to 0.

In an embodiment, the encoding the at least one chrominance QP offsetinto the bitstream based on the JCCR control flag may comprise:

encoding, based on the JCCR control flag, the at least one chrominanceQP offset into a picture parameter set, PPS, level syntax of thebitstream.

In an embodiment, the PPS level syntax may comprise the followingstructure:

pic_parameter_set_rbsp( ) { Descriptor ...  pps_cb_qp_offset se(v) pps_cr_qp_offset se(v)  if( sps_joint_cbcr_enabled_flag )  pps_joint_cbcr_qp_offset se(v)  cu_chroma_qp_offset_enabled_flag u(1) if( pps_cu_chroma_qp_offset_list_enabled_flag ) {  cu_chroma_qp_offset_subdiv ue(v)   chroma_qp_offset_list_len_minus1ue(v)   for( i = 0; i <= chroma_qp_offset_list_len_minus1;   i++ ) {   cb_qp_offset_list[ i ] se(v)    cr_qp_offset_list[ i ] se(v)    if(sps_joint_cbcr_enabled_flag )     joint_cbcr_qp_offset_list[ i ] se(v)  }  } ... }

The present disclosure may further provide, in an embodiment, a methodfor inverse quantization of a current block of a picture, wherein themethod is performed by an encoder, the method comprising:

encoding syntax elements from Slice Header and PPS syntax into abitstream, wherein the syntax elements comprise at least one chrominancequantization parameter, QP, offset;

encoding chrominance QP offset information from the Slice Header intothe bitstream, wherein the QP offset information is obtainedindependently of any PPS syntax elements in the PPS syntax;

providing the bitstream.

In an embodiment, the at least one chrominance QP offset encoded fromthe PPS syntax may comprise: pps_cb_qp_offset, pps_cr_qp_offset,pps_joint_cbcr_qp_offset, and cu_chroma_qp_offset_enabled_flag.

In an embodiment, if the value of the cu_chroma_qp_offset_enabled_flagis 1, the at least one chrominance QP offsets encoded from the PPSsyntax further may further comprise: cu_chroma_qp_offset_subdiv,chroma_qp_offset_list_len_minus1, cb_qp_offset_list[i],cr_qp_offset_list[i] and joint_cbcr_qp_offset_list[i], wherein0≤i≤chroma_qp_offset_list_len_minus1 and i is a integer.

In an embodiment, the chrominance QP offset information encoded from theSlice Header syntax may comprise: slice_cb_qp_offset andslice_cr_qp_offset.

In an embodiment, if the value of sps_joint_cbcr_enabled_flag comprisedin the bitstream is 1, the chrominance QP offset information encodedfrom the Slice Header syntax may further comprise:slice_joint_cbcr_qp_offset.

In an embodiment, the PPS syntax may comprise the following structure:

pic_parameter_set_rbsp( ) { Descriptor ...  pps_cb_qp_offset se(v) pps_cr_qp_offset se(v)  pps_joint_cbcr_qp_offset se(v) cu_chroma_qp_offset_enabled_flag u(1)  if(cu_chroma_qp_offset_enabled_flag ) {   cu_chroma_qp_offset_subdiv ue(v)  chroma_qp_offset_list_len_minus1 ue(v)   for( i = 0; i <=chroma_qp_offset_list_len_minus1;   i++ ) {    cb_qp_offset_list[ i ]se(v)    cr_qp_offset_list[ i ] se(v)    joint_cbcr_qp_offset_list[ i ]se(v)   }  } ... }

In an embodiment, the slice header syntax may comprise the followingstructure:

slice_header( ) { Descriptor ...  slice_cb_qp_offset se(v) slice_cr_qp_offset se(v)  if( sps_joint_cbcr_enabled_flag )  slice_joint_cbcr_qp_offset se(v) ... }

In an embodiment, the flag pps_slice_chroma_qp_offsets_present flag maybe omitted in the PPS syntax; or

the Slice Header and the PPS syntax may always comprise elements relatedto the at least one chrominance QP offset.

The present disclosure further provides a decoder comprising processingcircuitry for carrying out the method according to an embodiment.

The present disclosure further provides an encoder comprising processingcircuitry for carrying out an embodiment.

The present disclosure also provides a computer program productcomprising program code for performing an embodiment, when executed on acomputer or a processor.

The present disclosure further provides a decoder, comprising: one ormore processors; and a non-transitory computer-readable storage mediumcoupled to the processors and storing programming for execution by theprocessors, wherein the programming, when executed by the processors,configures the decoder to carry out an embodiment.

The present disclosure further provides an encoder, comprising: one ormore processors; and

a non-transitory computer-readable storage medium coupled to theprocessors and storing programming for execution by the processors,wherein the programming, when executed by the processors, configures theencoder to carry out an embodiment.

The present disclosure further provides a non-transitorycomputer-readable medium carrying a program code which, when executed bya computer device, causes the computer device to perform an embodiment.

The present disclosure further provides a decoder, comprising: areceiving unit configured to receive a bitstream; a first obtaining unitconfigured to obtain a joint chrominance component residual, JCCR,control flag from the bitstream; a second obtaining unit configured toobtain a chrominance mapping information from the bitstream based on theJCCR control flag; a third obtaining unit configured to obtain at leastone chrominance quantization parameter, (QP, offset from the bitstreambased on the JCCR control flag; a fourth obtaining unit configured toobtain a QP value for the current chrominance block based on theobtained chrominance mapping information and the at least one obtainedchrominance QP offset; an inverse quantizing unit configured to performinverse quantization on the current chrominance block by using thedetermined QP value.

In an embodiment the bitstream may comprise an SPS level syntax, and theJCCR control flag may be obtained from the SPS level syntax.

In an embodiment, the JCCR control flag may be thesps_joint_cbcr_enabled_flag.

In an embodiment, if the value of the sps_joint_cbcr_enabled_flag is 1,the at least one obtained chrominance QP offset may be specified byslice_joint_cbcr_qp_offset.

In an embodiment, the chrominance mapping information may comprisedelta_qp_in_val_minus1[i][j] and delta_qp_out_val[i][j], and thechrominance mapping information may be obtained from an SPS level syntaxcomprised in the bitstream.

In an embodiment, the SPS level syntax may comprise the followingstructure:

seq_parameter_set_rbsp( ) { Descriptor ...   same_qp_table_for_chromau(1)   for( i = 0; i < same_qp_table_for_chroma ? 1 : sps_joint_  cbcr_enabled_flag ? 3 : 2; i++ ) {    num_points_in_qp_table_minus1[ i] ue(v)    for( j = 0; j <= num_points_in_qp_table_minus1[ i ];    j++ ){     delta_qp_in_val_minus1[ i ][ j ] ue(v) ... ue(v)    }   }  } ... }

In an embodiment, the obtaining the at least one chrominance QP offsetfrom the bitstream based on the JCCR control flag may compriseobtaining, based on the JCCR control flag, the at least one chrominanceQP offset from a picture parameter set, PPS, level syntax of thebitstream.

In an embodiment, the PPS level syntax may comprise the followingstructure:

pic_parameter_set_rbsp( ) { Descriptor ...  pps_cb_qp_offset se(v) pps_cr_qp_offset se(v)  if( sps_joint_cbcr_enabled_flag )  pps_joint_cbcr_qp_offset se(v)  cu_chroma_qp_offset_enabled_flag u(1) if( pps_cu_chroma_qp_offset_list_enabled_flag ) {  cu_chroma_qp_offset_subdiv ue(v)   chroma_qp_offset_list_len_minus1ue(v)   for( i = 0; i <= chroma_qp_offset_list_len_minus1;   i++ ) {   cb_qp_offset_list[ i ] se(v)    cr_qp_offset_list[ i ] se(v)    if(sps_joint_cbcr_enabled_flag )     joint_cbcr_qp_offset_list[ i ] se(v)  }  } ... }

The present disclosure further provides, in an embodiment, a decoder,comprising: a receiving unit configured to receive a bitstream, whereinthe bitstream comprises a Slice Header syntax and a PPS syntax; a firstobtaining unit configured to obtain syntax elements from the PPS syntax,wherein the obtained syntax elements comprises chrominance quantizationparameter, QP, offsets; a second obtaining unit configured to obtainchrominance QP offset information from the Slice Header, wherein the QPoffset information is obtained independently of any PPS syntax elementsin the PPS syntax; a determining unit configured to determining a QPvalue for the current chrominance block depending on the chrominance QPoffset obtained from the PPS syntax and the chrominance QP offsetinformation obtained from the Slice Header syntax; an inversequantization unit configured to perform inverse quantization on thecurrent chrominance block by using the determined QP value.

In an embodiment, the at least one chrominance QP offset obtained fromthe PPS syntax may comprise: pps_cb_qp_offset, pps_cr_qp_offset,pps_joint_cbcr_qp_offset, and cu_chroma_qp_offset_enabled_flag.

In an embodiment, if the value of the cu_chroma_qp_offset_enabled_flagis 1, the at least one chrominance QP offset obtained from the PPSsyntax further may comprise: cu_chroma_qp_offset_subdiv,chroma_qp_offset_list_len_minus1, cb_qp_offset_list[i],cr_qp_offset_list[i] and joint_cbcr_qp_offset_list[i], wherein0≤i≤chroma_qp_offset_list_len_minus1 and i is a integer.

In an embodiment, the chrominance QP offset information obtained fromthe Slice Header syntax may comprise: slice_cb_qp_offset andslice_cr_qp_offset.

In an embodiment, if the value of sps_joint_cbcr_enabled_flag comprisedin the bitstream is 1, the chrominance QP offset information obtainedfrom the Slice Header syntax may further comprise:slice_joint_cbcr_qp_offset.

In an embodiment, the PPS syntax may comprise the following structure:

pic_parameter_set_rbsp( ) { Descriptor ...  pps_cb_qp_offset se(v) pps_cr_qp_offset se(v)  pps_joint_cbcr_qp_offset se(v) cu_chroma_qp_offset_enabled_flag u(1)  if(cu_chroma_qp_offset_enabled_flag ) {   cu_chroma_qp_offset_subdiv ue(v)  chroma_qp_offset_list_len_minus1 ue(v)   for( i = 0; i <=chroma_qp_offset_list_len_minus1;   i++ ) {    cb_qp_offset_list[ i ]se(v)    cr_qp_offset_list[ i ] se(v)    joint_cbcr_qp_offset_list[ i ]se(v)   }  } ... }

In an embodiment, the slice header syntax may comprise the followingstructure:

slice_header( ) { Descriptor ...  slice_cb_qp_offset se(v) slice_cr_qp_offset se(v)  if( sps_joint_cbcr_enabled_flag )  slice_joint_cbcr_qp_offset se(v) ... }

In an embodiment, the flag pps_slice_chroma_qp_offsets_present_flag maybe omitted in the PPS syntax; or

the Slice Header and the PPS syntax may always comprise elements relatedto the at least one chrominance QP offset.

The present disclosure further provides, in an embodiment, an encoder,comprising: a first encoding unit configured to encode a jointchrominance component residual, JCCR, control flag into a bitstream; asecond encoding unit configured to encode a chrominance mappinginformation into the bitstream based on the JCCR control flag; a thirdencoding unit configured to encode at least one chrominance quantizationparameter, (QP, offset into the bitstream based on the JCCR controlflag; a providing unit configured to provide the bitstream.

In an embodiment, the bitstream may comprise an SPS level syntax, andthe JCCR control flag may be obtained from the SPS level syntax.

In an embodiment, the JCCR control flag may be thesps_joint_cbcr_enabled_flag.

In an embodiment, if the value of the sps_joint_cbcr_enabled_flag is 1,the at least one obtained chrominance QP offset may be specified byslice_joint_cbcr_qp_offset.

In an embodiment, the chrominance mapping information may comprisedelta_qp_in_val_minus1[i][j] and delta_qp_out_val[i][j], and thechrominance mapping information may be obtained from an SPS level syntaxcomprised in the bitstream.

In an embodiment, the SPS level syntax may comprise the followingstructure:

seq_parameter_set_rbsp( ) { Descriptor ...   same_qp_table_for_chromau(1)   for( i = 0; i < same_qp_table_for_chroma ? 1 : sps_  joint_cbcr_enabled_flag ? 3 : 2; i++ ) {   num_points_in_qp_table_minus1[ i ] ue(v)    for( j = 0; j <=num_points_in_qp_table_minus1[ i ];    j++ ) {    delta_qp_in_val_minus1[ i ][ j ] ue(v) ... ue(v)    }   }  } ... }

In an embodiment, the obtaining the at least one chrominance QP offsetfrom the bitstream based on the JCCR control flag may compriseobtaining, based on the JCCR control flag, the at least one chrominanceQP offset from a picture parameter set, PPS, level syntax of thebitstream.

In an embodiment, the PPS level syntax may comprise the followingstructure:

pic_parameter_set_rbsp( ) { Descriptor ...  pps_cb_qp_offset se(v) pps_cr_qp_offset se(v)  if( sps_joint_cbcr_enabled_flag )  pps_joint_cbcr_qp_offset se(v)  cu_chroma_qp_offset_enabled_flag u(1) if( pps_cu_chroma_qp_offset_list_enabled_flag ) {  cu_chroma_qp_offset_subdiv ue(v)   chroma_qp_offset_list_len_minus1ue(v)   for( i = 0; i <= chroma_qp_offset_list_len_minus1;   i++ ) {   cb_qp_offset_list[ i ] se(v)    cr_qp_offset_list[ i ] se(v)    if(sps_joint_cbcr_enabled_flag )     joint_cbcr_qp_offset_list[ i ] se(v)  }  } ... }

The present disclosure further provides, in an embodiment, an encoder,comprising: a first encoding unit configured to encode syntax elementsfrom Slice Header and PPS syntax into the bitstream, wherein the syntaxelements comprise chrominance quantization parameter, QP, offsets; asecond encoding unit configured to encode chrominance QP offsetinformation from the Slice Header into the bitstream, wherein the QPoffset information is obtained independently of any PPS syntax elementsin the PPS syntax; a providing unit configured to provide the bitstream.

In an embodiment, the at least one chrominance QP offset obtained fromthe PPS syntax may comprise: pps_cb_qp_offset, pps_cr_qp_offset,pps_joint_cbcr_qp_offset, and cu_chroma_qp_offset_enabled_flag.

In an embodiment, if the value of the cu_chroma_qp_offset_enabled_flagis 1, the at least one chrominance QP offset obtained from the PPSsyntax further may comprise: cu_chroma_qp_offset_subdiv,chroma_qp_offset_list_len_minus1, cb_qp_offset_list[i],cr_qp_offset_list[i] and joint_cbcr_qp_offset_list[i], wherein0≤i≤chroma_qp_offset_list_len_minus1 and i is a integer.

In an embodiment, the chrominance QP offset information obtained fromthe Slice Header syntax may comprise: slice_cb_qp_offset andslice_cr_qp_offset.

In an embodiment, if the value of sps_joint_cbcr_enabled_flag comprisedin the bitstream is 1, the chrominance QP offset information obtainedfrom the Slice Header syntax may further comprise:slice_joint_cbcr_qp_offset.

In an embodiment, the PPS syntax may comprise the following structure:

pic_parameter_set_rbsp( ) { Descriptor ...  pps_cb_qp_offset se(v) pps_cr_qp_offset se(v)  pps_joint_cbcr_qp_offset se(v) cu_chroma_qp_offset_enabled_flag u(1)  if( cu_chroma_qp_offset_ enabled_flag ) {   cu_chroma_qp_offset_subdiv ue(v)  chroma_qp_offset_list_len_minus1 ue(v)   for( i = 0; i <=chroma_qp_offset_list_   len_minus1; i++ ) {    cb_qp_offset_list[ i ]se(v)    cr_qp_offset_list[ i ] se(v)    joint_cbcr_qp_offset_list[ i ]se(v)   }  } ... }

In an embodiment, the slice header syntax may comprise the followingstructure:

Descriptor slice header( ) { ...  slice_cb_qp_offset se (v) slice_cr_qp_offset se (v)  if( sps_joint_cbcr_enabled_flag )  slice_joint_cbcr_qp_offset se (v) ... }

In an embodiment, the flag pps_slice_chroma_qp_offsets_present_flag maybe omitted in the PPS syntax; or

the Slice Header and the PPS syntax may always comprise elements relatedto the at least one chrominance QP offset.

Details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following embodiments of the disclosure are described in moredetail with reference to the attached figures and drawings, in which:

FIG. 1A is a block diagram showing an example of a video coding systemconfigured to implement embodiments of the disclosure.

FIG. 1B is a block diagram showing another example of a video codingsystem configured to implement embodiments of the disclosure.

FIG. 2 is a block diagram showing an example of a video encoderconfigured to implement embodiments of the disclosure.

FIG. 3 is a block diagram showing an example structure of a videodecoder configured to implement embodiments of the disclosure.

FIG. 4 is a block diagram illustrating an example of an encodingapparatus or a decoding apparatus.

FIG. 5 is a block diagram illustrating another example of an encodingapparatus or a decoding apparatus.

FIG. 6 is a block diagram showing an example structure of a contentsupply system 3100, which realizes a content delivery service.

FIG. 7 is a block diagram showing a structure of an example of aterminal device.

FIG. 8 illustrates a flowchart of a method for inverse quantization of acurrent block of a picture, the method being performed by a decoder,according to an embodiment of the present disclosure.

FIG. 9 illustrates a flowchart of a method for inverse quantization of acurrent block of a picture, the method being performed by a decoder,according to a further embodiment of the present disclosure.

FIG. 10 illustrates a flowchart of a method for inverse quantization ofa current block of a picture, the method being performed by an encoder,according to an embodiment of the present disclosure.

FIG. 11 illustrates a flowchart of a method for inverse quantization ofa current block of a picture, the method being performed by an encoder,according to an embodiment the present disclosure.

FIG. 12 illustrates a decoder according to an embodiment of the presentdisclosure.

FIG. 13 illustrates a decoder according to another embodiment of thepresent disclosure.

FIG. 14 illustrates an encoder according to an embodiment of the presentdisclosure.

FIG. 15 illustrates an encoder according to another embodiment of thepresent disclosure.

In the following, identical reference signs refer to identical or atleast functionally equivalent features if not explicitly specifiedotherwise.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, reference is made to the accompanyingfigures, which form part of the disclosure, and which show, by way ofillustration, specific aspects of embodiments of the disclosure orspecific aspects in which embodiments of the present disclosure may beused. It is understood that embodiments of the disclosure may be used inother aspects and comprise structural or logical changes not depicted inthe figures. The following detailed description, therefore, is not to betaken in a limiting sense, and the scope of the present disclosure isdefined by the appended claims.

For instance, it is understood that a disclosure in connection with adescribed method may also hold true for a corresponding device or systemconfigured to perform the method and vice versa. For example, if one ora plurality of specific method steps are described, a correspondingdevice may include one or a plurality of units, e.g. functional units,to perform the described one or plurality of method steps (e.g. one unitperforming the one or plurality of steps, or a plurality of units eachperforming one or more of the plurality of steps), even if such one ormore units are not explicitly described or illustrated in the figures.On the other hand, for example, if a specific apparatus is describedbased on one or a plurality of units, e.g. functional units, acorresponding method may include one step to perform the functionalityof the one or plurality of units (e.g. one step performing thefunctionality of the one or plurality of units, or a plurality of stepseach performing the functionality of one or more of the plurality ofunits), even if such one or plurality of steps are not explicitlydescribed or illustrated in the figures. Further, it is understood thatthe features of the various exemplary embodiments and/or aspectsdescribed herein may be combined with each other, unless specificallynoted otherwise.

Video coding typically refers to the processing of a sequence ofpictures, which form the video or video sequence. Instead of the term“picture” the term “frame” or “image” may be used as synonyms in thefield of video coding. Video coding (or coding in general) comprises twoparts video encoding and video decoding. Video encoding is performed atthe source side, typically comprising processing (e.g. by compression)the original video pictures to reduce the amount of data required forrepresenting the video pictures (for more efficient storage and/ortransmission). Video decoding is performed at the destination side andtypically comprises the inverse processing compared to the encoder toreconstruct the video pictures. Embodiments referring to “coding” ofvideo pictures (or pictures in general) shall be understood to relate to“encoding” or “decoding” of video pictures or respective videosequences. The combination of the encoding part and the decoding part isalso referred to as CODEC (Coding and Decoding).

In case of lossless video coding, the original video pictures can bereconstructed, i.e. the reconstructed video pictures have the samequality as the original video pictures (assuming no transmission loss orother data loss during storage or transmission). In case of lossy videocoding, further compression, e.g. by quantization, is performed, toreduce the amount of data representing the video pictures, which cannotbe completely reconstructed at the decoder, i.e. the quality of thereconstructed video pictures is lower or worse compared to the qualityof the original video pictures.

Several video coding standards belong to the group of “lossy hybridvideo codecs” (i.e. combine spatial and temporal prediction in thesample domain and 2D transform coding for applying quantization in thetransform domain). Each picture of a video sequence is typicallypartitioned into a set of non-overlapping blocks and the coding istypically performed on a block level. In other words, at the encoder thevideo is typically processed, i.e. encoded, on a block (video block)level, e.g. by using spatial (intra picture) prediction and/or temporal(inter picture) prediction to generate a prediction block, subtractingthe prediction block from the current block (block currentlyprocessed/to be processed) to obtain a residual block, transforming theresidual block and quantizing the residual block in the transform domainto reduce the amount of data to be transmitted (compression), whereas atthe decoder the inverse processing compared to the encoder is applied tothe encoded or compressed block to reconstruct the current block forrepresentation. Furthermore, the encoder duplicates the decoderprocessing loop such that both will generate identical predictions (e.g.intra- and inter predictions) and/or re-constructions for processing,i.e. coding, the subsequent blocks.

In the following, embodiments of a video coding system 10, a videoencoder 20 and a video decoder 30 are described based on FIGS. 1 to 3.

FIG. 1A is a schematic block diagram illustrating an example codingsystem 10, e.g. a video coding system 10 (or short coding system 10)that may utilize techniques of this present application. Video encoder20 (or short encoder 20) and video decoder 30 (or short decoder 30) ofvideo coding system 10 represent examples of devices that may beconfigured to perform techniques in accordance with various examplesdescribed in the present application.

As shown in FIG. 1A, the coding system 10 comprises a source device 12configured to provide encoded picture data 21 e.g. to a destinationdevice 14 for decoding the encoded picture data 13.

The source device 12 comprises an encoder 20, and may additionally, i.e.optionally, comprise a picture source 16, a pre-processor (orpre-processing unit) 18, e.g. a picture pre-processor 18, and acommunication interface or communication unit 22.

The picture source 16 may comprise or be any kind of picture capturingdevice, for example a camera for capturing a real-world picture, and/orany kind of a picture generating device, for example a computer-graphicsprocessor for generating a computer animated picture, or any kind ofother device for obtaining and/or providing a real-world picture, acomputer generated picture (e.g. a screen content, a virtual reality(VR) picture) and/or any combination thereof (e.g. an augmented reality(AR) picture). The picture source may be any kind of memory or storagestoring any of the aforementioned pictures.

In distinction to the pre-processor 18 and the processing performed bythe pre-processing unit 18, the picture or picture data 17 may also bereferred to as raw picture or raw picture data 17.

Pre-processor 18 is configured to receive the (raw) picture data 17 andto perform pre-processing on the picture data 17 to obtain apre-processed picture 19 or pre-processed picture data 19.Pre-processing performed by the pre-processor 18 may, e.g., comprisetrimming, color format conversion (e.g. from RGB to YCbCr), colorcorrection, or de-noising. It can be understood that the pre-processingunit 18 may be optional component.

The video encoder 20 is configured to receive the pre-processed picturedata 19 and provide encoded picture data 21 (further details will bedescribed below, e.g., based on FIG. 2).

Communication interface 22 of the source device 12 may be configured toreceive the encoded picture data 21 and to transmit the encoded picturedata 21 (or any further processed version thereof) over communicationchannel 13 to another device, e.g. the destination device 14 or anyother device, for storage or direct reconstruction.

The destination device 14 comprises a decoder 30 (e.g. a video decoder30), and may additionally, i.e. optionally, comprise a communicationinterface or communication unit 28, a post-processor 32 (orpost-processing unit 32) and a display device 34.

The communication interface 28 of the destination device 14 isconfigured receive the encoded picture data 21 (or any further processedversion thereof), e.g. directly from the source device 12 or from anyother source, e.g. a storage device, e.g. an encoded picture datastorage device, and provide the encoded picture data 21 to the decoder30.

The communication interface 22 and the communication interface 28 may beconfigured to transmit or receive the encoded picture data 21 or encodeddata 13 via a direct communication link between the source device 12 andthe destination device 14, e.g. a direct wired or wireless connection,or via any kind of network, e.g. a wired or wireless network or anycombination thereof, or any kind of private and public network, or anykind of combination thereof.

The communication interface 22 may be, e.g., configured to package theencoded picture data 21 into an appropriate format, e.g. packets, and/orprocess the encoded picture data using any kind of transmission encodingor processing for transmission over a communication link orcommunication network.

The communication interface 28, forming the counterpart of thecommunication interface 22, may be, e.g., configured to receive thetransmitted data and process the transmission data using any kind ofcorresponding transmission decoding or processing and/or de-packaging toobtain the encoded picture data 21.

Both, communication interface 22 and communication interface 28 may beconfigured as unidirectional communication interfaces as indicated bythe arrow for the communication channel 13 in FIG. 1A pointing from thesource device 12 to the destination device 14, or bi-directionalcommunication interfaces, and may be configured, e.g. to send andreceive messages, e.g. to set up a connection, to acknowledge andexchange any other information related to the communication link and/ordata transmission, e.g. encoded picture data transmission.

The decoder 30 is configured to receive the encoded picture data 21 andprovide decoded picture data 31 or a decoded picture 31 (further detailswill be described below, e.g., based on FIG. 3 or FIG. 5).

The post-processor 32 of destination device 14 is configured topost-process the decoded picture data 31 (also called reconstructedpicture data), e.g. the decoded picture 31, to obtain post-processedpicture data 33, e.g. a post-processed picture 33. The post-processingperformed by the post-processing unit 32 may comprise, e.g. color formatconversion (e.g. from YCbCr to RGB), color correction, trimming, orre-sampling, or any other processing, e.g. for preparing the decodedpicture data 31 for display, e.g. by display device 34.

The display device 34 of the destination device 14 is configured toreceive the post-processed picture data 33 for displaying the picture,e.g. to a user or viewer. The display device 34 may be or comprise anykind of display for representing the reconstructed picture, e.g. anintegrated or external display or monitor. The displays may, e.g.comprise liquid crystal displays (LCD), organic light emitting diodes(OLED) displays, plasma displays, projectors, micro LED displays, liquidcrystal on silicon (LCoS), digital light processor (DLP) or any kind ofother display.

Although FIG. 1A depicts the source device 12 and the destination device14 as separate devices, embodiments of devices may also comprise both orboth functionalities, the source device 12 or correspondingfunctionality and the destination device 14 or correspondingfunctionality. In such embodiments the source device 12 or correspondingfunctionality and the destination device 14 or correspondingfunctionality may be implemented using the same hardware and/or softwareor by separate hardware and/or software or any combination thereof.

As will be apparent for the skilled person based on the description, theexistence and (exact) split of functionalities of the different units orfunctionalities within the source device 12 and/or destination device 14as shown in FIG. 1A may vary depending on the actual device andapplication.

The encoder 20 (e.g. a video encoder 20) or the decoder 30 (e.g. a videodecoder 30) or both encoder 20 and decoder 30 may be implemented viaprocessing circuitry as shown in FIG. 1B, such as one or moremicroprocessors, digital signal processors (DSPs), application-specificintegrated circuits (ASICs), field-programmable gate arrays (FPGAs),discrete logic, hardware, video coding dedicated or any combinationsthereof. The encoder 20 may be implemented via processing circuitry 46to embody the various modules as discussed with respect to encoder 20 ofFIG. 2 and/or any other encoder system or subsystem described herein.The decoder 30 may be implemented via processing circuitry 46 to embodythe various modules as discussed with respect to decoder 30 of FIG. 3and/or any other decoder system or subsystem described herein. Theprocessing circuitry may be configured to perform the various operationsas discussed later. As shown in FIG. 5, if the techniques areimplemented partially in software, a device may store instructions forthe software in a suitable, non-transitory computer-readable storagemedium and may execute the instructions in hardware using one or moreprocessors to perform the techniques of this disclosure. Either of videoencoder 20 and video decoder 30 may be integrated as part of a combinedencoder/decoder (CODEC) in a single device, for example, as shown inFIG. 1B.

Source device 12 and destination device 14 may comprise any of a widerange of devices, including any kind of handheld or stationary devices,e.g. notebook or laptop computers, mobile phones, smart phones, tabletsor tablet computers, cameras, desktop computers, set-top boxes,televisions, display devices, digital media players, video gamingconsoles, video streaming devices (such as content services servers orcontent delivery servers), broadcast receiver device, broadcasttransmitter device, or the like and may use no or any kind of operatingsystem. In some cases, the source device 12 and the destination device14 may be equipped for wireless communication. Thus, the source device12 and the destination device 14 may be wireless communication devices.

In some cases, video coding system 10 illustrated in FIG. 1A is merelyan example and the techniques of the present application may apply tovideo coding settings (e.g., video encoding or video decoding) that donot necessarily include any data communication between the encoding anddecoding devices. In other examples, data is retrieved from a localmemory, streamed over a network, or the like. A video encoding devicemay encode and store data to memory, and/or a video decoding device mayretrieve and decode data from memory. In some examples, the encoding anddecoding is performed by devices that do not communicate with oneanother, but simply encode data to memory and/or retrieve and decodedata from memory.

For convenience of description, embodiments of the disclosure aredescribed herein, for example, by reference to High-Efficiency VideoCoding (HEVC) or to the reference software of Versatile Video coding(VVC), the next generation video coding standard developed by the JointCollaboration Team on Video Coding (JCT-VC) of ITU-T Video CodingExperts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG).One of ordinary skill in the art will understand that embodiments of thedisclosure are not limited to HEVC or VVC.

Encoder and Encoding Method

FIG. 2 shows a schematic block diagram of an example video encoder 20that is configured to implement the techniques of the presentapplication. In the example of FIG. 2, the video encoder 20 comprises aninput 201 (or input interface 201), a residual calculation unit 204, atransform processing unit 206, a quantization unit 208, an inversequantization unit 210, and inverse transform processing unit 212, areconstruction unit 214, a loop filter unit 220, a decoded picturebuffer (DPB) 230, a mode selection unit 260, an entropy encoding unit270 and an output 272 (or output interface 272). The mode selection unit260 may include an inter prediction unit 244, an intra prediction unit254 and a partitioning unit 262. Inter prediction unit 244 may include amotion estimation unit and a motion compensation unit (not shown). Avideo encoder 20 as shown in FIG. 2 may also be referred to as hybridvideo encoder or a video encoder according to a hybrid video codec.

The residual calculation unit 204, the transform processing unit 206,the quantization unit 208, the mode selection unit 260 may be referredto as forming a forward signal path of the encoder 20, whereas theinverse quantization unit 210, the inverse transform processing unit212, the reconstruction unit 214, the buffer 216, the loop filter 220,the decoded picture buffer (DPB) 230, the inter prediction unit 244 andthe intra-prediction unit 254 may be referred to as forming a backwardsignal path of the video encoder 20, wherein the backward signal path ofthe video encoder 20 corresponds to the signal path of the decoder (seevideo decoder 30 in FIG. 3). The inverse quantization unit 210, theinverse transform processing unit 212, the reconstruction unit 214, theloop filter 220, the decoded picture buffer (DPB) 230, the interprediction unit 244 and the intra-prediction unit 254 are also referredto forming the “built-in decoder” of video encoder 20.

Pictures & Picture Partitioning (Pictures & Blocks)

The encoder 20 may be configured to receive, e.g. via input 201, apicture 17 (or picture data 17), e.g. picture of a sequence of picturesforming a video or video sequence. The received picture or picture datamay also be a pre-processed picture 19 (or pre-processed picture data19). For sake of simplicity the following description refers to thepicture 17. The picture 17 may also be referred to as current picture orpicture to be coded (in particular in video coding to distinguish thecurrent picture from other pictures, e.g. previously encoded and/ordecoded pictures of the same video sequence, i.e. the video sequencewhich also comprises the current picture).

A (digital) picture is or can be regarded as a two-dimensional array ormatrix of samples with intensity values. A sample in the array may alsobe referred to as pixel (short form of picture element) or a pel. Thenumber of samples in horizontal and vertical direction (or axis) of thearray or picture define the size and/or resolution of the picture. Forrepresentation of color, typically three color components are employed,i.e. the picture may be represented or include three sample arrays. InRBG format or color space a picture comprises a corresponding red, greenand blue sample array. However, in video coding each pixel is typicallyrepresented in a luminance and chrominance format or color space, e.g.YCbCr, which comprises a luminance component indicated by Y (sometimesalso L is used instead) and two chrominance components indicated by Cband Cr. The luminance (or short luma) component Y represents thebrightness or grey level intensity (e.g. like in a grey-scale picture),while the two chrominance (or short chroma) components Cb and Crrepresent the chromaticity or color information components. Accordingly,a picture in YCbCr format comprises a luminance sample array ofluminance sample values (Y), and two chrominance sample arrays ofchrominance values (Cb and Cr). Pictures in RGB format may be convertedor transformed into YCbCr format and vice versa, the process is alsoknown as color transformation or conversion. If a picture is monochrome,the picture may comprise only a luminance sample array. Accordingly, apicture may be, for example, an array of luma samples in monochromeformat or an array of luma samples and two corresponding arrays ofchroma samples in 4:2:0, 4:2:2, and 4:4:4 colour format.

Embodiments of the video encoder 20 may comprise a picture partitioningunit (not depicted in FIG. 2) configured to partition the picture 17into a plurality of (typically non-overlapping) picture blocks 203.These blocks may also be referred to as root blocks, macro blocks(H.264/AVC) or coding tree blocks (CTB) or coding tree units (CTU)(H.265/HEVC and VVC). The picture partitioning unit may be configured touse the same block size for all pictures of a video sequence and thecorresponding grid defining the block size, or to change the block sizebetween pictures or subsets or groups of pictures, and partition eachpicture into the corresponding blocks.

In further embodiments, the video encoder may be configured to receivedirectly a block 203 of the picture 17, e.g. one, several or all blocksforming the picture 17. The picture block 203 may also be referred to ascurrent picture block or picture block to be coded.

Like the picture 17, the picture block 203 again is or can be regardedas a two-dimensional array or matrix of samples with intensity values(sample values), although of smaller dimension than the picture 17. Inother words, the block 203 may comprise, e.g., one sample array (e.g. aluma array in case of a monochrome picture 17, or a luma or chroma arrayin case of a color picture) or three sample arrays (e.g. a luma and twochroma arrays in case of a color picture 17) or any other number and/orkind of arrays depending on the color format applied. The number ofsamples in horizontal and vertical direction (or axis) of the block 203define the size of block 203. Accordingly, a block may, for example, anM×N (M-column by N-row) array of samples, or an M×N array of transformcoefficients.

Embodiments of the video encoder 20 as shown in FIG. 2 may be configuredto encode the picture 17 block by block, e.g. the encoding andprediction is performed per block 203.

Embodiments of the video encoder 20 as shown in FIG. 2 may be furtherconfigured to partition and/or encode the picture by using slices (alsoreferred to as video slices), wherein a picture may be partitioned intoor encoded using one or more slices (typically non-overlapping), andeach slice may comprise one or more blocks (e.g. CTUs) or one or moregroups of blocks (e.g. tiles (H.265/HEVC and VVC) or bricks (VVC)).

Embodiments of the video encoder 20 as shown in FIG. 2 may be furtherconfigured to partition and/or encode the picture by using slices/tilegroups (also referred to as video tile groups) and/or tiles (alsoreferred to as video tiles), wherein a picture may be partitioned intoor encoded using one or more slices/tile groups (typicallynon-overlapping), and each slice/tile group may comprise, e.g. one ormore blocks (e.g. CTUs) or one or more tiles, wherein each tile, e.g.may be of rectangular shape and may comprise one or more blocks (e.g.CTUs), e.g. complete or fractional blocks.

Residual Calculation

The residual calculation unit 204 may be configured to calculate aresidual block 205 (also referred to as residual 205) based on thepicture block 203 and a prediction block 265 (further details about theprediction block 265 are provided later), e.g. by subtracting samplevalues of the prediction block 265 from sample values of the pictureblock 203, sample by sample (pixel by pixel) to obtain the residualblock 205 in the sample domain.

Transform

The transform processing unit 206 may be configured to apply atransform, e.g. a discrete cosine transform (DCT) or discrete sinetransform (DST), on the sample values of the residual block 205 toobtain transform coefficients 207 in a transform domain. The transformcoefficients 207 may also be referred to as transform residualcoefficients and represent the residual block 205 in the transformdomain.

The transform processing unit 206 may be configured to apply integerapproximations of DCT/DST, such as the transforms specified forH.265/HEVC. Compared to an orthogonal DCT transform, such integerapproximations are typically scaled by a certain factor. In order topreserve the norm of the residual block which is processed by forwardand inverse transforms, additional scaling factors are applied as partof the transform process. The scaling factors are typically chosen basedon certain constraints like scaling factors being a power of two forshift operations, bit depth of the transform coefficients, tradeoffbetween accuracy and implementation costs, etc. Specific scaling factorsare, for example, specified for the inverse transform, e.g. by inversetransform processing unit 212 (and the corresponding inverse transform,e.g. by inverse transform processing unit 312 at video decoder 30) andcorresponding scaling factors for the forward transform, e.g. bytransform processing unit 206, at an encoder 20 may be specifiedaccordingly.

Embodiments of the video encoder 20 (respectively transform processingunit 206) may be configured to output transform parameters, e.g. a typeof transform or transforms, e.g. directly or encoded or compressed viathe entropy encoding unit 270, so that, e.g., the video decoder 30 mayreceive and use the transform parameters for decoding.

Quantization

The quantization unit 208 may be configured to quantize the transformcoefficients 207 to obtain quantized coefficients 209, e.g. by applyingscalar quantization or vector quantization. The quantized coefficients209 may also be referred to as quantized transform coefficients 209 orquantized residual coefficients 209.

The quantization process may reduce the bit depth associated with someor all of the transform coefficients 207. For example, an n-bittransform coefficient may be rounded down to an m-bit Transformcoefficient during quantization, where n is greater than m. The degreeof quantization may be modified by adjusting a quantization parameter(QP). For example for scalar quantization, different scaling may beapplied to achieve finer or coarser quantization. Smaller quantizationstep sizes correspond to finer quantization, whereas larger quantizationstep sizes correspond to coarser quantization. The applicablequantization step size may be indicated by a quantization parameter(QP). The quantization parameter may for example be an index to apredefined set of applicable quantization step sizes. For example, smallquantization parameters may correspond to fine quantization (smallquantization step sizes) and large quantization parameters maycorrespond to coarse quantization (large quantization step sizes) orvice versa. The quantization may include division by a quantization stepsize and a corresponding and/or the inverse dequantization, e.g. byinverse quantization unit 210, may include multiplication by thequantization step size. Embodiments according to some standards, e.g.HEVC, may be configured to use a quantization parameter to determine thequantization step size. Generally, the quantization step size may becalculated based on a quantization parameter using a fixed pointapproximation of an equation including division. Additional scalingfactors may be introduced for quantization and dequantization to restorethe norm of the residual block, which might get modified because of thescaling used in the fixed point approximation of the equation forquantization step size and quantization parameter. In one exampleimplementation, the scaling of the inverse transform and dequantizationmight be combined. Alternatively, customized quantization tables may beused and signaled from an encoder to a decoder, e.g. in a bitstream. Thequantization is a lossy operation, wherein the loss increases withincreasing quantization step sizes.

Basic quantization parameter in signalled in the bitstream for all lumaand chroma components together. However, quantization parameters forchrominance components can be shifted from the basic one at thepictures/slices or tiles groups inside one picture/coding unit insideone slice or tile group levels. For this purpose the bitstream cancontain PPS offsets for two chrominance components (pps_cb_qp_offset andpps_cr_qp_offset syntax elements); slice offsets for two chrominancecomponents (slice_cb_qp_offset and slice_cr_qp_offset); and two offsetlists (cb_qp_offset_list and cr_qp_offset_list), which are normallysignaled in PPS and allow to apply QP offset for CU level by sending atCU level index pointing to the tables.

Embodiments of the video encoder 20 (respectively quantization unit 208)may be configured to output quantization parameters (QP), e.g. directlyor encoded via the entropy encoding unit 270, so that, e.g., the videodecoder 30 may receive and apply the quantization parameters fordecoding.

Inverse Quantization

The inverse quantization unit 210 is configured to apply the inversequantization of the quantization unit 208 on the quantized coefficientsto obtain dequantized coefficients 211, e.g. by applying the inverse ofthe quantization scheme applied by the quantization unit 208 based on orusing the same quantization step size as the quantization unit 208. Thedequantized coefficients 211 may also be referred to as dequantizedresidual coefficients 211 and correspond—although typically notidentical to the transform coefficients due to the loss byquantization—to the transform coefficients 207.

Inverse Transform

The inverse transform processing unit 212 is configured to apply theinverse transform of the transform applied by the transform processingunit 206, e.g. an inverse discrete cosine transform (DCT) or inversediscrete sine transform (DST) or other inverse transforms, to obtain areconstructed residual block 213 (or corresponding dequantizedcoefficients 213) in the sample domain. The reconstructed residual block213 may also be referred to as transform block 213.

Reconstruction

The reconstruction unit 214 (e.g. adder or summer 214) is configured toadd the transform block 213 (i.e. reconstructed residual block 213) tothe prediction block 265 to obtain a reconstructed block 215 in thesample domain, e.g. by adding—sample by sample—the sample values of thereconstructed residual block 213 and the sample values of the predictionblock 265.

Filtering

The loop filter unit 220 (or short “loop filter” 220), is configured tofilter the reconstructed block 215 to obtain a filtered block 221, or ingeneral, to filter reconstructed samples to obtain filtered samplevalues. The loop filter unit is, e.g., configured to smooth pixeltransitions, or otherwise improve the video quality. The loop filterunit 220 may comprise one or more loop filters such as a de-blockingfilter, a sample-adaptive offset (SAO) filter or one or more otherfilters, e.g. an adaptive loop filter (ALF), a noise suppression filter(NSF), or any combination thereof. In an example, the loop filter unit220 may comprise a de-blocking filter, a SAO filter and an ALF filter.The order of the filtering process may be the deblocking filter, SAO andALF. In another example, a process called the luma mapping with chromascaling (LMCS) (namely, the adaptive in-loop reshaper) is added. Thisprocess is performed before deblocking. In another example, thedeblocking filter process may be also applied to internal sub-blockedges, e.g. affine sub-blocks edges, ATMVP sub-blocks edges, sub-blocktransform (SBT) edges and intra sub-partition (ISP) edges. Although theloop filter unit 220 is shown in FIG. 2 as being an in loop filter, inother configurations, the loop filter unit 220 may be implemented as apost loop filter. The filtered block 221 may also be referred to asfiltered reconstructed block 221.

Embodiments of the video encoder 20 (respectively loop filter unit 220)may be configured to output loop filter parameters (such as SAO filterparameters or ALF filter parameters or LMCS parameters), e.g. directlyor encoded via the entropy encoding unit 270, so that, e.g., a decoder30 may receive and apply the same loop filter parameters or respectiveloop filters for decoding.

Decoded Picture Buffer

The decoded picture buffer (DPB) 230 may be a memory that storesreference pictures, or in general reference picture data, for encodingvideo data by video encoder 20. The DPB 230 may be formed by any of avariety of memory devices, such as dynamic random access memory (DRAM),including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. The decodedpicture buffer (DPB) 230 may be configured to store one or more filteredblocks 221. The decoded picture buffer 230 may be further configured tostore other previously filtered blocks, e.g. previously reconstructedand filtered blocks 221, of the same current picture or of differentpictures, e.g. previously reconstructed pictures, and may providecomplete previously reconstructed, i.e. decoded, pictures (andcorresponding reference blocks and samples) and/or a partiallyreconstructed current picture (and corresponding reference blocks andsamples), for example for inter prediction. The decoded picture buffer(DPB) 230 may be also configured to store one or more unfilteredreconstructed blocks 215, or in general unfiltered reconstructedsamples, e.g. if the reconstructed block 215 is not filtered by loopfilter unit 220, or any other further processed version of thereconstructed blocks or samples.

Mode Selection (Partitioning & Prediction)

The mode selection unit 260 comprises partitioning unit 262,inter-prediction unit 244 and intra-prediction unit 254, and isconfigured to receive or obtain original picture data, e.g. an originalblock 203 (current block 203 of the current picture 17), andreconstructed picture data, e.g. filtered and/or unfilteredreconstructed samples or blocks of the same (current) picture and/orfrom one or a plurality of previously decoded pictures, e.g. fromdecoded picture buffer 230 or other buffers (e.g. line buffer, notshown). The reconstructed picture data is used as reference picture datafor prediction, e.g. inter-prediction or intra-prediction, to obtain aprediction block 265 or predictor 265.

Mode selection unit 260 may be configured to determine or select apartitioning for a current block prediction mode (including nopartitioning) and a prediction mode (e.g. an intra or inter predictionmode) and generate a corresponding prediction block 265, which is usedfor the calculation of the residual block 205 and for the reconstructionof the reconstructed block 215.

Embodiments of the mode selection unit 260 may be configured to selectthe partitioning and the prediction mode (e.g. from those supported byor available for mode selection unit 260), which provide the best matchor in other words the minimum residual (minimum residual means bettercompression for transmission or storage), or a minimum signalingoverhead (minimum signaling overhead means better compression fortransmission or storage), or which considers or balances both. The modeselection unit 260 may be configured to determine the partitioning andprediction mode based on rate distortion optimization (RDO), i.e. selectthe prediction mode, which provides a minimum rate distortion. Termslike “best”, “minimum”, “optimum” etc. in this context do notnecessarily refer to an overall “best”, “minimum”, “optimum”, etc. butmay also refer to the fulfillment of a termination or selectioncriterion like a value exceeding or falling below a threshold or otherconstraints leading potentially to a “sub-optimum selection” butreducing complexity and processing time.

In other words, the partitioning unit 262 may be configured to partitiona picture from a video sequence into a sequence of coding tree units(CTUs), and the CTU 203 may be further partitioned into smaller blockpartitions or sub-blocks (which form again blocks), e.g. iterativelyusing quad-tree-partitioning (QT), binary partitioning (BT) ortriple-tree-partitioning (TT) or any combination thereof, and toperform, e.g., the prediction for each of the block partitions orsub-blocks, wherein the mode selection comprises the selection of thetree-structure of the partitioned block 203 and the prediction modes areapplied to each of the block partitions or sub-blocks.

In the following the partitioning (e.g. by partitioning unit 260) andprediction processing (by inter-prediction unit 244 and intra-predictionunit 254) performed by an example video encoder 20 will be explained inmore detail.

Partitioning

The partitioning unit 262 may be configured to partition a picture froma video sequence into a sequence of coding tree units (CTUs), and thepartitioning unit 262 may partition (or split) a coding tree unit (CTU)203 into smaller partitions, e.g. smaller blocks of square orrectangular size. For a picture that has three sample arrays, a CTUconsists of an N×N block of luma samples together with two correspondingblocks of chroma samples. The maximum allowed size of the luma block ina CTU is specified to be 128×128 in the developing versatile videocoding (VVC), but it can be specified to be value rather than 128×128 inthe future, for example, 256×256. The CTUs of a picture may beclustered/grouped as slices/tile groups, tiles or bricks. A tile coversa rectangular region of a picture, and a tile can be divided into one ormore bricks. A brick consists of a number of CTU rows within a tile. Atile that is not partitioned into multiple bricks can be referred to asa brick. However, a brick is a true subset of a tile and is not referredto as a tile. There are two modes of tile groups are supported in VVC,namely the raster-scan slice/tile group mode and the rectangular slicemode. In the raster-scan tile group mode, a slice/tile group contains asequence of tiles in tile raster scan of a picture. In the rectangularslice mode, a slice contains a number of bricks of a picture thatcollectively form a rectangular region of the picture. The bricks withina rectangular slice are in the order of brick raster scan of the slice.These smaller blocks (which may also be referred to as sub-blocks) maybe further partitioned into even smaller partitions. This is alsoreferred to tree-partitioning or hierarchical tree-partitioning, whereina root block, e.g. at root tree-level 0 (hierarchy-level 0, depth 0),may be recursively partitioned, e.g. partitioned into two or more blocksof a next lower tree-level, e.g. nodes at tree-level 1 (hierarchy-level1, depth 1), wherein these blocks may be again partitioned into two ormore blocks of a next lower level, e.g. tree-level 2 (hierarchy-level 2,depth 2), etc. until the partitioning is terminated, e.g. because atermination criterion is fulfilled, e.g. a maximum tree depth or minimumblock size is reached. Blocks, which are not further partitioned, arealso referred to as leaf-blocks or leaf nodes of the tree. A tree usingpartitioning into two partitions is referred to as binary-tree (BT), atree using partitioning into three partitions is referred to asternary-tree (TT), and a tree using partitioning into four partitions isreferred to as quad-tree (QT).

For example, a coding tree unit (CTU) may be or comprise a CTB of lumasamples, two corresponding CTBs of chroma samples of a picture that hasthree sample arrays, or a CTB of samples of a monochrome picture or apicture that is coded using three separate colour planes and syntaxstructures used to code the samples. Correspondingly, a coding treeblock (CTB) may be an N×N block of samples for some value of N such thatthe division of a component into CTBs is a partitioning. A coding unit(CU) may be or comprise a coding block of luma samples, twocorresponding coding blocks of chroma samples of a picture that hasthree sample arrays, or a coding block of samples of a monochromepicture or a picture that is coded using three separate colour planesand syntax structures used to code the samples. Correspondingly, acoding block (CB) may be an M×N block of samples for some values of Mand N such that the division of a CTB into coding blocks is apartitioning.

In embodiments, e.g., according to HEVC, a coding tree unit (CTU) may besplit into CUs by using a quad-tree structure denoted as coding tree.The decision whether to code a picture area using inter-picture(temporal) or intra-picture (spatial) prediction is made at the leaf CUlevel. Each leaf CU can be further split into one, two or four PUsaccording to the PU splitting type. Inside one PU, the same predictionprocess is applied and the relevant information is transmitted to thedecoder on a PU basis. After obtaining the residual block by applyingthe prediction process based on the PU splitting type, a leaf CU can bepartitioned into transform units (TUs) according to another quadtreestructure similar to the coding tree for the CU.

In embodiments, e.g., according to the latest video coding standardcurrently in development, which is referred to as Versatile Video Coding(VVC), a combined Quad-tree nested multi-type tree using binary andternary splits segmentation structure for example used to partition acoding tree unit. In the coding tree structure within a coding treeunit, a CU can have either a square or rectangular shape. For example,the coding tree unit (CTU) is first partitioned by a quaternary tree.Then the quaternary tree leaf nodes can be further partitioned by amulti-type tree structure. There are four splitting types in multi-typetree structure, vertical binary splitting (SPLIT_BT_VER), horizontalbinary splitting (SPLIT_BT_HOR), vertical ternary splitting(SPLIT_TT_VER), and horizontal ternary splitting (SPLIT_TT_HOR). Themulti-type tree leaf nodes are called coding units (CUs), and unless theCU is too large for the maximum transform length, this segmentation isused for prediction and transform processing without any furtherpartitioning. This means that, in most cases, the CU, PU and TU have thesame block size in the quadtree with nested multi-type tree coding blockstructure. The exception occurs when maximum supported transform lengthis smaller than the width or height of the colour component of theCU.VVC develops a unique signaling mechanism of the partition splittinginformation in quadtree with nested multi-type tree coding treestructure. In the signalling mechanism, a coding tree unit (CTU) istreated as the root of a quaternary tree and is first partitioned by aquaternary tree structure. Each quaternary tree leaf node (whensufficiently large to allow it) is then further partitioned by amulti-type tree structure. In the multi-type tree structure, a firstflag (mtt_split_cu_flag) is signalled to indicate whether the node isfurther partitioned; when a node is further partitioned, a second flag(mtt_split_cu_vertical_flag) is signalled to indicate the splittingdirection, and then a third flag (mtt_split_cu_binary_flag) is signalledto indicate whether the split is a binary split or a ternary split.Based on the values of mtt_split_cu_vertical_flag andmtt_split_cu_binary_flag, the multi-type tree slitting mode(MttSplitMode) of a CU can be derived by a decoder based on a predefinedrule or a table. It should be noted, for a certain design, for example,64×64 Luma block and 32×32 Chroma pipelining design in VVC hardwaredecoders, TT split is forbidden when either width or height of a lumacoding block is larger than 64, as shown in FIG. 6. TT split is alsoforbidden when either width or height of a chroma coding block is largerthan 32. The pipelining design will divide a picture into Virtualpipeline data units (VPDUs) which are defined as non-overlapping unitsin a picture. In hardware decoders, successive VPDUs are processed bymultiple pipeline stages simultaneously. The VPDU size is roughlyproportional to the buffer size in most pipeline stages, so it isimportant to keep the VPDU size small. In most hardware decoders, theVPDU size can be set to maximum transform block (TB) size. However, inVVC, ternary tree (TT) and binary tree (BT) partition may lead to theincreasing of VPDUs sizes

In addition, it should be noted that, when a portion of a tree nodeblock exceeds the bottom or right picture boundary, the tree node blockis forced to be split until the all samples of every coded CU arelocated inside the picture boundaries.

As an example, the Intra Sub-Partitions (ISP) tool may divide lumaintra-predicted blocks vertically or horizontally into 2 or 4sub-partitions depending on the block size.

In one example, the mode selection unit 260 of video encoder 20 may beconfigured to perform any combination of the partitioning techniquesdescribed herein.

As described above, the video encoder 20 is configured to determine orselect the best or an optimum prediction mode from a set of (e.g.pre-determined) prediction modes. The set of prediction modes maycomprise, e.g., intra-prediction modes and/or inter-prediction modes.

Intra-Prediction

The set of intra-prediction modes may comprise 35 differentintra-prediction modes, e.g. non-directional modes like DC (or mean)mode and planar mode, or directional modes, e.g. as defined in HEVC, ormay comprise 67 different intra-prediction modes, e.g. non-directionalmodes like DC (or mean) mode and planar mode, or directional modes, e.g.as defined for VVC. As an example, several conventional angular intraprediction modes are adaptively replaced with wide-angle intraprediction modes for the non-square blocks, e.g. as defined in VVC. Asanother example, to avoid division operations for DC prediction, onlythe longer side is used to compute the average for non-square blocks.Moreover, the results of intra prediction of planar mode may be furthermodified by a position dependent intra prediction combination (PDPC)method.

The intra-prediction unit 254 is configured to use reconstructed samplesof neighboring blocks of the same current picture to generate anintra-prediction block 265 according to an intra-prediction mode of theset of intra-prediction modes.

The intra prediction unit 254 (or in general the mode selection unit260) is further configured to output intra-prediction parameters (or ingeneral information indicative of the selected intra prediction mode forthe block) to the entropy encoding unit 270 in form of syntax elements266 for inclusion into the encoded picture data 21, so that, e.g., thevideo decoder 30 may receive and use the prediction parameters fordecoding.

Inter-Prediction

The set of (or possible) inter-prediction modes depends on the availablereference pictures (i.e. previous at least partially decoded pictures,e.g. stored in DBP 230) and other inter-prediction parameters, e.g.whether the whole reference picture or only a part, e.g. a search windowarea around the area of the current block, of the reference picture isused for searching for a best matching reference block, and/or e.g.whether pixel interpolation is applied, e.g. half/semi-pel, quarter-peland/or 1/16 pel interpolation, or not.

Additional to the above prediction modes, skip mode, direct mode and/orother inter prediction mode may be applied.

For example, Extended merge prediction, the merge candidate list of suchmode is constructed by including the following five types of candidatesin order: Spatial MVP from spatial neighbor CUs, Temporal MVP fromcollocated CUs, History-based MVP from an FIFO table, Pairwise averageMVP and Zero MVs. In addition, a bilateral-matching based decoder sidemotion vector refinement (DMVR) may be applied to increase the accuracyof the MVs of the merge mode. Merge mode with MVD (MMVD), which comesfrom merge mode with motion vector differences. A MMVD flag is signaledright after sending a skip flag and merge flag to specify whether MMVDmode is used for a CU. In addition, a CU-level adaptive motion vectorresolution (AMVR) scheme may be applied. AMVR allows MVD of the CU to becoded in different precision. Dependent on the prediction mode for thecurrent CU, the MVDs of the current CU can be adaptively selected. Whena CU is coded in merge mode, the combined inter/intra prediction (CIIP)mode may be applied to the current CU. Weighted averaging of the interand intra prediction signals is performed to obtain the CIIP prediction.Affine motion compensated prediction, the affine motion field of theblock is described by motion information of two control point(4-parameter) or three control point motion vectors (6-parameter).Subblock-based temporal motion vector prediction (SbTMVP), which issimilar to the temporal motion vector prediction (TMVP) in HEVC, butpredicts the motion vectors of the sub-CUs within the current CU.Bi-directional optical flow (BDOF), previously referred to as BIO, is asimpler version that requires much less computation, especially in termsof number of multiplications and the size of the multiplier. Trianglepartition mode, in such a mode, a CU is split evenly into twotriangle-shaped partitions, using either the diagonal split or theanti-diagonal split. Besides, the bi-prediction mode is extended beyondsimple averaging to allow weighted averaging of the two predictionsignals.

The inter prediction unit 244 may include a motion estimation (ME) unitand a motion compensation (MC) unit (both not shown in FIG. 2). Themotion estimation unit may be configured to receive or obtain thepicture block 203 (current picture block 203 of the current picture 17)and a decoded picture 231, or at least one or a plurality of previouslyreconstructed blocks, e.g. reconstructed blocks of one or a plurality ofother/different previously decoded pictures 231, for motion estimation.E.g., a video sequence may comprise the current picture and thepreviously decoded pictures 231, or in other words, the current pictureand the previously decoded pictures 231 may be part of or form asequence of pictures forming a video sequence.

The encoder 20 may, e.g., be configured to select a reference block froma plurality of reference blocks of the same or different pictures of theplurality of other pictures and provide a reference picture (orreference picture index) and/or an offset (spatial offset) between theposition (x, y coordinates) of the reference block and the position ofthe current block as inter prediction parameters to the motionestimation unit. This offset is also called motion vector (MV).

The motion compensation unit is configured to obtain, e.g. receive, aninter prediction parameter and to perform inter prediction based on orusing the inter prediction parameter to obtain an inter prediction block265. Motion compensation, performed by the motion compensation unit, mayinvolve fetching or generating the prediction block based on themotion/block vector determined by motion estimation, possibly performinginterpolations to sub-pixel precision. Interpolation filtering maygenerate additional pixel samples from known pixel samples, thuspotentially increasing the number of candidate prediction blocks thatmay be used to code a picture block. Upon receiving the motion vectorfor the PU of the current picture block, the motion compensation unitmay locate the prediction block to which the motion vector points in oneof the reference picture lists.

The motion compensation unit may also generate syntax elementsassociated with the blocks and video slices for use by video decoder 30in decoding the picture blocks of the video slice. In addition or as analternative to slices and respective syntax elements, tile groups and/ortiles and respective syntax elements may be generated or used.

Entropy Coding

The entropy encoding unit 270 is configured to apply, for example, anentropy encoding algorithm or scheme (e.g. a variable length coding(VLC) scheme, an context adaptive VLC scheme (CAVLC), an arithmeticcoding scheme, a binarization, a context adaptive binary arithmeticcoding (CABAC), syntax-based context-adaptive binary arithmetic coding(SBAC), probability interval partitioning entropy (PIPE) coding oranother entropy encoding methodology or technique) or bypass (nocompression) on the quantized coefficients 209, inter predictionparameters, intra prediction parameters, loop filter parameters and/orother syntax elements to obtain encoded picture data 21 which can beoutput via the output 272, e.g. in the form of an encoded bitstream 21,so that, e.g., the video decoder 30 may receive and use the parametersfor decoding. The encoded bitstream 21 may be transmitted to videodecoder 30, or stored in a memory for later transmission or retrieval byvideo decoder 30.

Other structural variations of the video encoder 20 can be used toencode the video stream. For example, a non-transform based encoder 20can quantize the residual signal directly without the transformprocessing unit 206 for certain blocks or frames. In anotherimplementation, an encoder 20 can have the quantization unit 208 and theinverse quantization unit 210 combined into a single unit.

Decoder and Decoding Method

FIG. 3 shows an example of a video decoder 30 that is configured toimplement the techniques of this present application. The video decoder30 is configured to receive encoded picture data 21 (e.g. encodedbitstream 21), e.g. encoded by encoder 20, to obtain a decoded picture331. The encoded picture data or bitstream comprises information fordecoding the encoded picture data, e.g. data that represents pictureblocks of an encoded video slice (and/or tile groups or tiles) andassociated syntax elements.

In the example of FIG. 3, the decoder 30 comprises an entropy decodingunit 304, an inverse quantization unit 310, an inverse transformprocessing unit 312, a reconstruction unit 314 (e.g. a summer 314), aloop filter 320, a decoded picture buffer (DBP) 330, a mode applicationunit 360, an inter prediction unit 344 and an intra prediction unit 354.Inter prediction unit 344 may be or include a motion compensation unit.Video decoder 30 may, in some examples, perform a decoding passgenerally reciprocal to the encoding pass described with respect tovideo encoder 100 from FIG. 2.

As explained with regard to the encoder 20, the inverse quantizationunit 210, the inverse transform processing unit 212, the reconstructionunit 214, the loop filter 220, the decoded picture buffer (DPB) 230, theinter prediction unit 344 and the intra prediction unit 354 are alsoreferred to as forming the “built-in decoder” of video encoder 20.Accordingly, the inverse quantization unit 310 may be identical infunction to the inverse quantization unit 110, the inverse transformprocessing unit 312 may be identical in function to the inversetransform processing unit 212, the reconstruction unit 314 may beidentical in function to reconstruction unit 214, the loop filter 320may be identical in function to the loop filter 220, and the decodedpicture buffer 330 may be identical in function to the decoded picturebuffer 230. Therefore, the explanations provided for the respectiveunits and functions of the video 20 encoder apply correspondingly to therespective units and functions of the video decoder 30.

Entropy Decoding

The entropy decoding unit 304 is configured to parse the bitstream 21(or in general encoded picture data 21) and perform, for example,entropy decoding to the encoded picture data 21 to obtain, e.g.,quantized coefficients 309 and/or decoded coding parameters (not shownin FIG. 3), e.g. any or all of inter prediction parameters (e.g.reference picture index and motion vector), intra prediction parameter(e.g. intra prediction mode or index), transform parameters,quantization parameters, loop filter parameters, and/or other syntaxelements. Entropy decoding unit 304 maybe configured to apply thedecoding algorithms or schemes corresponding to the encoding schemes asdescribed with regard to the entropy encoding unit 270 of the encoder20. Entropy decoding unit 304 may be further configured to provide interprediction parameters, intra prediction parameter and/or other syntaxelements to the mode application unit 360 and other parameters to otherunits of the decoder 30. Video decoder 30 may receive the syntaxelements at the video slice level and/or the video block level. Inaddition or as an alternative to slices and respective syntax elements,tile groups and/or tiles and respective syntax elements may be receivedand/or used.

Inverse Quantization

The inverse quantization unit 310 may be configured to receivequantization parameters (QP) (or in general information related to theinverse quantization) and quantized coefficients from the encodedpicture data 21 (e.g. by parsing and/or decoding, e.g. by entropydecoding unit 304) and to apply based on the quantization parameters aninverse quantization on the decoded quantized coefficients 309 to obtaindequantized coefficients 311, which may also be referred to as transformcoefficients 311. The inverse quantization process may include use of aquantization parameter determined by video encoder 20 for each videoblock in the video slice (or tile or tile group) to determine a degreeof quantization and, likewise, a degree of inverse quantization thatshould be applied.

Inverse Transform

Inverse transform processing unit 312 may be configured to receivedequantized coefficients 311, also referred to as transform coefficients311, and to apply a transform to the dequantized coefficients 311 inorder to obtain reconstructed residual blocks 213 in the sample domain.The reconstructed residual blocks 213 may also be referred to astransform blocks 313. The transform may be an inverse transform, e.g.,an inverse DCT, an inverse DST, an inverse integer transform, or aconceptually similar inverse transform process. The inverse transformprocessing unit 312 may be further configured to receive transformparameters or corresponding information from the encoded picture data 21(e.g. by parsing and/or decoding, e.g. by entropy decoding unit 304) todetermine the transform to be applied to the dequantized coefficients311.

Reconstruction

The reconstruction unit 314 (e.g. adder or summer 314) may be configuredto add the reconstructed residual block 313, to the prediction block 365to obtain a reconstructed block 315 in the sample domain, e.g. by addingthe sample values of the reconstructed residual block 313 and the samplevalues of the prediction block 365.

Filtering

The loop filter unit 320 (either in the coding loop or after the codingloop) is configured to filter the reconstructed block 315 to obtain afiltered block 321, e.g. to smooth pixel transitions, or otherwiseimprove the video quality. The loop filter unit 320 may comprise one ormore loop filters such as a de-blocking filter, a sample-adaptive offset(SAO) filter or one or more other filters, e.g. an adaptive loop filter(ALF), a noise suppression filter (NSF), or any combination thereof. Inan example, the loop filter unit 220 may comprise a de-blocking filter,a SAO filter and an ALF filter. The order of the filtering process maybe the deblocking filter, SAO and ALF. In another example, a processcalled the luma mapping with chroma scaling (LMCS) (namely, the adaptivein-loop reshaper) is added. This process is performed before deblocking.In another example, the deblocking filter process may be also applied tointernal sub-block edges, e.g. affine sub-blocks edges, ATMVP sub-blocksedges, sub-block transform (SBT) edges and intra sub-partition (ISP)edges. Although the loop filter unit 320 is shown in FIG. 3 as being anin loop filter, in other configurations, the loop filter unit 320 may beimplemented as a post loop filter.

Decoded Picture Buffer

The decoded video blocks 321 of a picture are then stored in decodedpicture buffer 330, which stores the decoded pictures 331 as referencepictures for subsequent motion compensation for other pictures and/orfor output respectively display.

The decoder 30 is configured to output the decoded picture 311, e.g. viaoutput 312, for presentation or viewing to a user.

Prediction

The inter prediction unit 344 may be identical to the inter predictionunit 244 (in particular to the motion compensation unit) and the intraprediction unit 354 may be identical to the inter prediction unit 254 infunction, and performs split or partitioning decisions and predictionbased on the partitioning and/or prediction parameters or respectiveinformation received from the encoded picture data 21 (e.g. by parsingand/or decoding, e.g. by entropy decoding unit 304). Mode applicationunit 360 may be configured to perform the prediction (intra or interprediction) per block based on reconstructed pictures, blocks orrespective samples (filtered or unfiltered) to obtain the predictionblock 365.

When the video slice is coded as an intra coded (I) slice, intraprediction unit 354 of mode application unit 360 is configured togenerate prediction block 365 for a picture block of the current videoslice based on a signaled intra prediction mode and data from previouslydecoded blocks of the current picture. When the video picture is codedas an inter coded (i.e., B, or P) slice, inter prediction unit 344 (e.g.motion compensation unit) of mode application unit 360 is configured toproduce prediction blocks 365 for a video block of the current videoslice based on the motion vectors and other syntax elements receivedfrom entropy decoding unit 304. For inter prediction, the predictionblocks may be produced from one of the reference pictures within one ofthe reference picture lists. Video decoder 30 may construct thereference frame lists, List 0 and List 1, using default constructiontechniques based on reference pictures stored in DPB 330. The same orsimilar may be applied for or by embodiments using tile groups (e.g.video tile groups) and/or tiles (e.g. video tiles) in addition oralternatively to slices (e.g. video slices), e.g. a video may be codedusing I, P or B tile groups and/or tiles.

Mode application unit 360 is configured to determine the predictioninformation for a video block of the current video slice by parsing themotion vectors or related information and other syntax elements, anduses the prediction information to produce the prediction blocks for thecurrent video block being decoded. For example, the mode applicationunit 360 uses some of the received syntax elements to determine aprediction mode (e.g., intra or inter prediction) used to code the videoblocks of the video slice, an inter prediction slice type (e.g., Bslice, P slice, or GPB slice), construction information for one or moreof the reference picture lists for the slice, motion vectors for eachinter encoded video block of the slice, inter prediction status for eachinter coded video block of the slice, and other information to decodethe video blocks in the current video slice. The same or similar may beapplied for or by embodiments using tile groups (e.g. video tile groups)and/or tiles (e.g. video tiles) in addition or alternatively to slices(e.g. video slices), e.g. a video may be coded using I, P or B tilegroups and/or tiles.

Embodiments of the video decoder 30 as shown in FIG. 3 may be configuredto partition and/or decode the picture by using slices (also referred toas video slices), wherein a picture may be partitioned into or decodedusing one or more slices (typically non-overlapping), and each slice maycomprise one or more blocks (e.g. CTUs) or one or more groups of blocks(e.g. tiles (H.265/HEVC and VVC) or bricks (VVC)).

Embodiments of the video decoder 30 as shown in FIG. 3 may be configuredto partition and/or decode the picture by using slices/tile groups (alsoreferred to as video tile groups) and/or tiles (also referred to asvideo tiles), wherein a picture may be partitioned into or decoded usingone or more slices/tile groups (typically non-overlapping), and eachslice/tile group may comprise, e.g. one or more blocks (e.g. CTUs) orone or more tiles, wherein each tile, e.g. may be of rectangular shapeand may comprise one or more blocks (e.g. CTUs), e.g. complete orfractional blocks.

Other variations of the video decoder 30 can be used to decode theencoded picture data 21. For example, the decoder 30 can produce theoutput video stream without the loop filtering unit 320. For example, anon-transform based decoder 30 can inverse-quantize the residual signaldirectly without the inverse-transform processing unit 312 for certainblocks or frames. In another implementation, the video decoder 30 canhave the inverse-quantization unit 310 and the inverse-transformprocessing unit 312 combined into a single unit.

It should be understood that, in the encoder 20 and the decoder 30, aprocessing result of a current step may be further processed and thenoutput to the next step. For example, after interpolation filtering,motion vector derivation or loop filtering, a further operation, such asClip or shift, may be performed on the processing result of theinterpolation filtering, motion vector derivation or loop filtering.

It should be noted that further operations may be applied to the derivedmotion vectors of current block (including but not limit to controlpoint motion vectors of affine mode, sub-block motion vectors in affine,planar, ATMVP modes, temporal motion vectors, and so on). For example,the value of motion vector is constrained to a predefined rangeaccording to its representing bit. If the representing bit of motionvector is bitDepth, then the range is −2{circumflex over( )}(bitDepth−1)˜2{circumflex over ( )}(bitDepth−1)−1, where“{circumflex over ( )}” means exponentiation. For example, if bitDepthis set equal to 16, the range is −32768˜32767; if bitDepth is set equalto 18, the range is −131072{circumflex over ( )}131071. For example, thevalue of the derived motion vector (e.g. the MVs of four 4×4 sub-blockswithin one 8×8 block) is constrained such that the max differencebetween integer parts of the four 4×4 sub-block MVs is no more than Npixels, such as no more than 1 pixel. Here, two methods are provided forconstraining the motion vector according to the bitDepth.

FIG. 4 is a schematic diagram of a video coding device 400 according toan embodiment of the disclosure. The video coding device 400 is suitablefor implementing the disclosed embodiments as described herein. In anembodiment, the video coding device 400 may be a decoder such as videodecoder 30 of FIG. 1A or an encoder such as video encoder 20 of FIG. 1A.

The video coding device 400 comprises ingress ports 410 (or input ports410) and receiver units (Rx) 420 for receiving data; a processor, logicunit, or central processing unit (CPU) 430 to process the data;transmitter units (Tx) 440 and egress ports 450 (or output ports 450)for transmitting the data; and a memory 460 for storing the data. Thevideo coding device 400 may also comprise optical-to-electrical (OE)components and electrical-to-optical (EO) components coupled to theingress ports 410, the receiver units 420, the transmitter units 440,and the egress ports 450 for egress or ingress of optical or electricalsignals.

The processor 430 is implemented by hardware and software. The processor430 may be implemented as one or more CPU chips, cores (e.g., as amulti-core processor), FPGAs, ASICs, and DSPs. The processor 430 is incommunication with the ingress ports 410, receiver units 420,transmitter units 440, egress ports 450, and memory 460. The processor430 comprises a coding module 470. The coding module 470 implements thedisclosed embodiments described above. For instance, the coding module470 implements, processes, prepares, or provides the various codingoperations. The inclusion of the coding module 470 therefore provides asubstantial improvement to the functionality of the video coding device400 and effects a transformation of the video coding device 400 to adifferent state. Alternatively, the coding module 470 is implemented asinstructions stored in the memory 460 and executed by the processor 430.

The memory 460 may comprise one or more disks, tape drives, andsolid-state drives and may be used as an over-flow data storage device,to store programs when such programs are selected for execution, and tostore instructions and data that are read during program execution. Thememory 460 may be, for example, volatile and/or non-volatile and may bea read-only memory (ROM), random access memory (RAM), ternarycontent-addressable memory (TCAM), and/or static random-access memory(SRAM).

FIG. 5 is a simplified block diagram of an apparatus 500 that may beused as either or both of the source device 12 and the destinationdevice 14 from FIG. 1 according to an exemplary embodiment.

A processor 502 in the apparatus 500 can be a central processing unit.Alternatively, the processor 502 can be any other type of device, ormultiple devices, capable of manipulating or processing informationnow-existing or hereafter developed. Although the disclosedimplementations can be practiced with a single processor as shown, e.g.,the processor 502, advantages in speed and efficiency can be achievedusing more than one processor.

A memory 504 in the apparatus 500 can be a read only memory (ROM) deviceor a random access memory (RAM) device in an implementation. Any othersuitable type of storage device can be used as the memory 504. Thememory 504 can include code and data 506 that is accessed by theprocessor 502 using a bus 512. The memory 504 can further include anoperating system 508 and application programs 510, the applicationprograms 510 including at least one program that permits the processor502 to perform the methods described here. For example, the applicationprograms 510 can include applications 1 through N, which further includea video coding application that performs the methods described here.

The apparatus 500 can also include one or more output devices, such as adisplay 518. The display 518 may be, in one example, a touch sensitivedisplay that combines a display with a touch sensitive element that isoperable to sense touch inputs. The display 518 can be coupled to theprocessor 502 via the bus 512.

Although depicted here as a single bus, the bus 512 of the apparatus 500can be composed of multiple buses. Further, the secondary storage 514can be directly coupled to the other components of the apparatus 500 orcan be accessed via a network and can comprise a single integrated unitsuch as a memory card or multiple units such as multiple memory cards.The apparatus 500 can thus be implemented in a wide variety ofconfigurations.

Joint Coding of Chrominance Residuals (JVET-M0305)

Joint coding of chrominance residuals proposes a chrominance residualcoding mode where a single joint residual block is used to describe theresiduals of both Cb and Cr blocks in the same transform unit. Whenjoint residual mode is active, the indicated joint residual is added tothe Cb prediction block and deducted from the Cr prediction block. Inthe encoder side, the algorithm uses average of the positive Cb residualand negative Cr residual as the input to the transform and quantizationprocess.

The idea of joint coding of Cb and Cr is based on a fact that Cb and Crresiduals correlate inversely with each other. In this mode there is asingle residual indicated for the two chrominance blocks of a transformunit. The indicated residual is added to the prediction block in thefirst channel (typically representing Cb) and deducted from theprediction block in the second channel (typically representing Cr).

The joint residual mode is indicated with a flag in the bitstream if thecoded block flags (cbf) for both Cb and Cr are true. If the mode isactivated, a single residual block is decoded. The bitstream syntax anddecoding process of joint residual blocks follow those of the Cbresidual in VTM-3. The residuals of the Cr blocks are generated bynegating the decoded joint residual. As a single residual is used torepresent residuals of two blocks, the chroma QP offset parameter isreduce by 2 when the joint chrominance residual mode is active.

On the encoder side the average of positive Cb residual and negative Crresidual are used as the joint residual:

resJoint=(resCb−resCr)/2.

Joint Chroma Residual Coding with Multiple Modes (JVET-N0282)

Joint chroma residual coding with multiple modes is an extension of thejoint chroma residual coding suggested in JVET-M0305. In contrast toJVET-M0305, in which the addition of one joint chroma residual codingmode (given by Cr=−Cb) was suggested, this contribution proposes threemodes for joint chroma residual coding with different mixing factors(given by Cr=±Cb/2, Cr=±Cb, Cb=±Cr/2). The sign used for deriving thesecond chroma residual is coded in the tile group header. The usage of ajoint chroma coding mode is indicated by a TU-level flag and theselected mode is implicitly indicated by the chroma coded block flags.

Three modes for joint chroma residual coding are supported. In all ofthese three joint chroma residual coding modes, a single chromatransform block is coded (using the residual coding of VTM 4) and theother block of chroma residual samples is derived using simplearithmetic operations.

The following three joint chroma coding modes are supported:

Mode 1: Cb is coded and Cr is derived according to Cr=CSign*Cb/2;

Mode 2: Cb is coded and Cr is derived according to Cr=CSign*Cb;

Mode 3: Cr is coded and Cb is derived according to Cb=CSign*Cr/2,

where CSign represents the sign used for deriving the second chromaresidual block. CSign is indicated using a tile group header syntaxelement; it is either −1 or 1. Note that if CSign is equal to −1, mode 2is the same as the joint chroma coding mode suggested in JVET-M0305.

The usage of joint chroma residual coding is indicated by a TU-levelflag tu_joint_chroma_residual_flag. This flag is present if either orboth of the two chroma coded block flag (CBF) syntax elements are equalto 1. If tu_joint_chroma_residual_flag is equal to 1, one of the jointchroma residual coding modes is used. The mode used is indicated by thechroma CBFs, as specified in the following table:

joint chroma tu_cbf_cb tu_cbf_cr coding mode 1 0 mode 1 1 1 mode 2 0 1mode 3

If a joint chroma coding mode is chosen, the QP for coding the jointchroma component is decreased by 1 (for modes 1 and 3) or 2 (for mode2).

At the encoder side, the joint chroma residual is derived by acorresponding down-mixing of the Cb and Cr residuals. One of the threesupported chroma coding modes is pre-selected based on a minimization ofthe mixing distortion (i.e., the distortion obtained by firstdown-mixing the Cb and Cr residuals and then reconstructing, orup-mixing, the Cb and Cr residuals from the joint chroma residual,without quantization). Only the pre-selected mode is tested as anadditional mode in the mode decision process (i.e., using transform,quantization, and entropy coding). Due to the low-complexitypre-selection of one candidate mode for each TU, the encoding time isvirtually not changed relative to JVET-M0305.

The tile group header syntax element that indicates the sign (CSign) forderiving the second chroma component is determined by analyzing thecorrelation between high-pass filtered versions of the original Cb andCr components for the tile group.

Joint Chroma Residual Coding

The tests CE7-2.1/2 discuss extensions of the joint chroma residualcoding technique first described in JVET-M0305 by offering a wider rangeof joint-coding parameters and modes. Specifically, the following isdiscussed:

-   -   1) CE7-2.1: Extension of VTM 5.0 by allowing three instead of        one joint chroma coding mode as in JVET-N0282 configuration 1,        signaled using the chroma coded block flag (CBF) syntax        elements. These coding modes apply simplified cross-component        rotational transforms, as shown in Table 1.    -   2) CE7-2.2: Similar to CE7-2.1, but allowing two joint chroma        coded residual signals (instead of only one) to be transmitted        in case of the joint chroma coding mode signaled via CBF_(Cb)=1,        CBF_(Cr)=1. The rotational transform associated with this mode        represents a Hadamard transform, see Table 2.

Normative Reconstruction of Chroma Residuals

Thus, in contrast to M0305, in which the addition of one single-channeljoint chroma residual coding mode (given by Cr=−Cb) was suggested, inthe extensions, three modes for joint chroma residual coding withdifferent mixing factors are supported. The modes are additionallycharacterized by a sign (i. e., sign of the joint-decoding weights,CSign in JVET-N0282) used for deriving the second chroma residual, whichis coded in the slice header. The usage (activation) of a joint chromacoding mode is indicated by a TU-level flag tu_joint_cbcr_residual_flagand the selected mode is implicitly indicated by the chroma CBFs. Theflag tu_joint_cbcr_residual_flag is present if either or both chromaCBFs for a TU are equal to 1.

As in VTM 5.0, a chroma QP offset (coded at slice level) specificallyfor use with certain joint chroma coding modes can be signaled. When acorresponding joint chroma coding mode (modes 2 and 4 is the followingdescription) is active in a TU, this chroma QP offset is added to theapplied luma-derived chroma QP during quantization and decoding of thatTU. For the other modes (modes 1 and 3 in the following description),the chroma QPs are derived in the same way as for conventional Cb or Crblocks.

The normative reconstruction process of the chroma residuals (resCb andresCr) from the transmitted transform blocks (resJointC or, for CE7-2.2,resJointC1 and resJointC2) is summarized in the following tables.

TABLE 1 Reconstruction of chroma residuals in CE7-2.1. The value CSignis a sign value (+1 or −1), which is specified in the slice header,resJointC[ ][ ] is the transmitted residual. tu_cbf_cb tu_cbf_crreconstruction of Cb and Cr residuals mode 1 0 resCb[ x ][ y ] =resJointC[ x ][ y ] 1 resCr[ x ][ y ] = ( CSign * resJointC[ x ][ y ]) >> 1 1 1 resCb[ x ][ y ] = resJointC[ x ][ y ] 2 resCr[ x ][ y ] =CSign * resJointC[ x ][ y ] 0 1 resCb[ x ][ y ] = ( CSign * 3 resJointC[x ][ y ] ) >> 1 resCr[ x ][ y ] = resJointC[ x ][ y ]

TABLE 2 Reconstruction of chroma residuals in in CE7-2.2. The valueCSign is a sign value (+1 or −1) coded in the tile group header,resJointC1[ ][ ] are the transmitted residuals. The reconstruction forthe case tu_cbf_cb = 0, tu_cbf_cr = 1 depends on the value of the flagjoint_cbcr_alt_mode_flag, also transmitted in the slice header.tu_cbf_cb tu_cbf_cr reconstruction of Cb and Cr residuals mode 1 0resCb[ x ][ y ] = resJointC1[ x ][ y ] 2 resCr[ x ][ y ] = CSign *resJointC1[ x ][ y ] 1 1 resCb[ x ][ y ] = resJointC1[ x ][ y ] +resJointC2[ x ][ y ] 4 resCr[ x ][ y ] = CSign * ( resJointC1[ x ][ y ]− resJointC2[ x ][ y ] ) 0 1 if ( joint_cbcr_alt_mode_flag ) { 3  resCb[x ][ y ] = ( CSign * resJointC2[ x ][ y ] ) >> 1 1  resCr[ x ][ y ] =resJointC2[ x ][ y ] } else {  resCb[ x ][ y ] = resJointC2[ x ][ y ] resCr[ x ][ y ] = ( CSign * resJointC2[ x ][ y ] ) >> 1 }

Non-Normative Determination of Joint Chroma Residuals in the Encoder

In the investigated encoder implementation, the joint chroma componentsare derived as explained in the following. Depending on the mode (listedin the tables above), resJointC{1,2} are generated by the encoder asfollows:

-   -   If mode is equal to 4 (Hadamard transform, two residuals are        transmitted), the joint residuals are determined according to

resJointC1[x][y]=(resCb[x][y]+CSign*resCr[x][y])/2

resJointC2[x][y]=(resCb[x][y]−CSign*resCr[x][y])/2.

-   -   Otherwise, if mode is equal to 2 (single residual with        reconstruction Cb=C, Cr=CSign*C), the joint residual is        determined according to

resJointC[x][y]=(resCb[x][y]+CSign*resCr[x][y])/2.

-   -   Otherwise, if mode is equal to 1 (single residual with        reconstruction Cb=C, Cr=(CSign*C)/2), the joint residual is        determined according to

resJointC[x][y]=(4*resCb[x][y]+2*CSign*resCr[x][y])/5.

-   -   Otherwise (mode is equal to 3, i. e., single residual,        reconstruction Cr=C, Cb=(CSign*C)/2), the joint residual is        determined according to

resJointC[x][y]=(4*resCr[x][y]+2*CSign*resCb[x][y])/5.

More details on how the encoder selects the TU-wise joint mode are givenin Sec. 2.4 of JVET-N0282.

The First Embodiment of the Present Disclosure

In the first embodiment of the present disclosure, a signalling of PPSand Slice header QP offsets for chrominance component is performedindependently of each other's according to the following tables.

pic_parameter_set_rbsp( ) { Descriptor ...  pps_cb_qp_offset se(v) pps_cr_qp_offset se(v)  pps_joint_cbcr_qp_offset se(v) cu_chroma_qp_offset_enabled_flag u(1)  if( cu_chroma_qp_offset_ enabled_flag ) {   cu_chroma_qp_offset_subdiv ue(v)  chroma_qp_offset_list_len_minus1 ue(v)   for( i = 0; i <=chroma_qp_offset_   list_len_minus1; i++ ) {    cb_qp_offset_list[ i ]se(v)    cr_qp_offset_list[ i ] se(v)    joint_cbcr_qp_offset_list[ i ]se(v)   }  } ... }

slice_header( ) { Descriptor ...  slice_cb_qp_offset se(v) slice_cr_qp_offset se(v)  if( sps_joint_cbcr_enabled_flag )  slice_joint_cbcr_qp_offset se(v) ... }

Here, pic_parameter_set_rbsp refers to the Picture parameter set RBSPsyntax;

where pps_cb_qp_offset and pps_cr_qp_offset specify the offsets to theluma quantization parameter Qp′_(Y) used for deriving Qp′_(Cb) andQp′_(Cr), respectively;

wherein the values of pps_cb_qp_offset and pps_cr_qp_offset are in therange of −12 to +12, inclusive;

wherein when sps_chroma_format_idc is equal to 0, pps_cb_qp_offset andpps_cr_qp_offset are not used in the decoding process decoders shallignore their value;

wherein when not present, the values of pps_cb_qp_offset andpps_cr_qp_offset are inferred to be equal to 0;

wherein sps_joint_cbcr_enabled_flag equal to 1 specifies that the jointcoding of chroma residuals is enabled for a coded layer video sequence,CLVS,

where sps_joint_cbcr_enabled_flag equal to 0 specifies that the jointcoding of chroma residuals is disabled for the CLVS;

wherein when not present, the value of sps_joint_cbcr_enabled_flag isinferred to be equal to 0.

wherein pps_joint_cbcr_qp_offset_value specifies the offset to the lumaquantization parameter Qp′_(Y) used for deriving Qp′_(CbCr);

wherein the value of pps_joint_cbcr_qp_offset_value is in the range of−12 to +12, inclusive;

In the prior art, a flag pps_slice_chroma_qp_offsets_present_flag issignalled in PPS level syntax, which control whether there is anyfurther offsets signaling in slice header, that is, at the decoder side,the decoder need to check the value of thepps_slice_chroma_qp_offsets_present_flag to determine whether there isany further offsets signaled in the slice header. Comparing to the priorart, in the first embodiment, the flagpps_slice_chroma_qp_offsets_present flag is not signaled any more, inother words, there are offsets always signaled in the slice header,therefore, the decoder knows that there are further offsets signaled inthe slice header without check the value of thepps_slice_chroma_qp_offsets_present_flag, in other words, the PPS levelsyntax and the slice header syntax will always both include offsets.Thus, the decoding/signalling of chrominance QP offsets in slice headerbecomes simpler.

The Second Embodiment of the Present Disclosure

In the second embodiment of the present disclosure, a signalling of PPSand Slice header QP offsets for chrominance component for JCCR mode; anda signalling of SPS chrominance mapping information for JCCR coding modeis performed depending on SPS JCCR control flag according to thefollowing tables. For example, the sps JCCR control flag is thesps_joint_cbcr_enabled_flag signalled in SPS level syntax, e.g., theseq_parameter_set_rbsp syntax.

seq_parameter_set_rbsp( ) { Descriptor ...  if( ChromaArrayType != 0 ) {  same_qp_table_for_chroma u(1)   for( i = 0; i <same_qp_table_for_chroma ?   1 : sps_joint_cbcr_enabled_flag ? 3 : 2;i++ ) {    num_points_in_qp_table_minus1[ i ] ue(v)    for( j = 0; j <=num_points_in_    qp_table_minus1[ i ]; j++ ) {    delta_qp_in_val_minus1[ i ][ j ] ue(v)     delta_qp_out_val[ i ][ j] ue(v)    }   }  } ... }

It can be seen that, the value of “i” is determined based on the valueof sps_joint_cbcr_enabled_flag, thus redundant signalling of JCCR syntaxelements can be avoided when JCCR tool is disabled.

pic_parameter_set_rbsp( ) { Descriptor ...  pps_cb_qp_offset se(v) pps_cr_qp_offset se(v)  if( sps_joint_cbcr_enabled_flag )  pps_joint_cbcr_qp_offset se(v)  cu_chroma_qp_offset_enabled_flag u(1) if( cu_chroma_qp_offset_enabled_flag ) {   cu_chroma_qp_offset_subdivue(v)   chroma_qp_offset_list_len_minus1 ue(v)   for( i = 0; i <=chroma_qp_offset_   list_len_minus1; i++ ) {    cb_qp_offset_list[ i ]se(v)    cr_qp_offset_list[ i ] se(v)    if( sps_joint_cbcr_enabled_flag)     joint_cbcr_qp_offset_list[ i ] se(v)    }   } ... }

It can be seen that, the signalling/decoding of pps_joint_cbcr_qp_offsetis depending on sps_joint_cbcr_enabled_flag, that is, only when thevalue of sps_joint_cbcr_enabled_flag is true (e.g., 1), thepps_joint_cbcr_qp_offset will be signalled or can be decoded. Due to theconditioned signaling of pps_joint_cbcr_qp_offset, less information needto be signalled and thus can save resource.

slice_header( ) { Descriptor ...  slice_cb_qp_offset se(v) slice_cr_qp_offset se(v)  if( sps_joint_cbcr_enabled_flag )  slice_joint_cbcr_qp_offset se(v) ... }

Here, it should be noted that sps_joint_cbcr_enabled_flag equal to 1specifies that the joint coding of chroma residuals is enabled for acoded layer video sequence, CLVS, sps_joint_cbcr_enabled_flag equal to 0specifies that the joint coding of chroma residuals is disabled for thecode layer video sequence; wherein when not present, the value ofsps_joint_cbcr_enabled_flag is inferred to be equal to 0.

It should further be noted that where seq_parameter_set_rbsp refers tothe sequence parameter set Raw Byte Sequence Payload, RBSP, syntax;where sps_num_points_in_qp_table_minus1[i] plus 1 specifies the numberof points used to describe the i-th chroma QP mapping table; wherein thevalue of sps_num_points_in_qp_table_minus1[i] is in the range of 0 to36; wherein when not present, the value ofsps_num_points_in_qp_table_minus1[0] is inferred to be equal to 0.

Following is an explanation of the applications of the encoding methodas well as the decoding method as shown in the above-mentionedembodiments, and a system using them.

FIG. 6 is a block diagram showing a content supply system 3100 forrealizing content distribution service. This content supply system 3100includes capture device 3102, terminal device 3106, and optionallyincludes display 3126. The capture device 3102 communicates with theterminal device 3106 over communication link 3104. The communicationlink may include the communication channel 13 described above. Thecommunication link 3104 includes but not limited to WIFI, Ethernet,Cable, wireless (3G/4G/5G), USB, or any kind of combination thereof, orthe like.

The capture device 3102 generates data, and may encode the data by theencoding method as shown in the above embodiments. Alternatively, thecapture device 3102 may distribute the data to a streaming server (notshown in the Figures), and the server encodes the data and transmits theencoded data to the terminal device 3106. The capture device 3102includes but not limited to camera, smart phone or Pad, computer orlaptop, video conference system, PDA, vehicle mounted device, or acombination of any of them, or the like. For example, the capture device3102 may include the source device 12 as described above. When the dataincludes video, the video encoder 20 included in the capture device 3102may actually perform video encoding processing. When the data includesaudio (i.e., voice), an audio encoder included in the capture device3102 may actually perform audio encoding processing. For some practicalscenarios, the capture device 3102 distributes the encoded video andaudio data by multiplexing them together. For other practical scenarios,for example in the video conference system, the encoded audio data andthe encoded video data are not multiplexed. Capture device 3102distributes the encoded audio data and the encoded video data to theterminal device 3106 separately.

In the content supply system 3100, the terminal device 310 receives andreproduces the encoded data. The terminal device 3106 could be a devicewith data receiving and recovering capability, such as smart phone orPad 3108, computer or laptop 3110, network video recorder (NVR)/digitalvideo recorder (DVR) 3112, TV 3114, set top box (STB) 3116, videoconference system 3118, video surveillance system 3120, personal digitalassistant (PDA) 3122, vehicle mounted device 3124, or a combination ofany of them, or the like capable of decoding the above-mentioned encodeddata. For example, the terminal device 3106 may include the destinationdevice 14 as described above. When the encoded data includes video, thevideo decoder 30 included in the terminal device is prioritized toperform video decoding. When the encoded data includes audio, an audiodecoder included in the terminal device is prioritized to perform audiodecoding processing.

For a terminal device with its display, for example, smart phone or Pad3108, computer or laptop 3110, network video recorder (NVR)/digitalvideo recorder (DVR) 3112, TV 3114, personal digital assistant (PDA)3122, or vehicle mounted device 3124, the terminal device can feed thedecoded data to its display. For a terminal device equipped with nodisplay, for example, STB 3116, video conference system 3118, or videosurveillance system 3120, an external display 3126 is contacted thereinto receive and show the decoded data.

When each device in this system performs encoding or decoding, thepicture encoding device or the picture decoding device, as shown in theabove-mentioned embodiments, can be used.

FIG. 7 is a diagram showing a structure of an example of the terminaldevice 3106. After the terminal device 3106 receives stream from thecapture device 3102, the protocol proceeding unit 3202 analyzes thetransmission protocol of the stream. The protocol includes but notlimited to Real Time Streaming Protocol (RTSP), Hyper Text TransferProtocol (HTTP), HTTP Live streaming protocol (HLS), MPEG-DASH,Real-time Transport protocol (RTP), Real Time Messaging Protocol (RTMP),or any kind of combination thereof, or the like.

After the protocol proceeding unit 3202 processes the stream, streamfile is generated. The file is outputted to a demultiplexing unit 3204.The demultiplexing unit 3204 can separate the multiplexed data into theencoded audio data and the encoded video data. As described above, forsome practical scenarios, for example in the video conference system,the encoded audio data and the encoded video data are not multiplexed.In this situation, the encoded data is transmitted to video decoder 3206and audio decoder 3208 without through the demultiplexing unit 3204.

Via the demultiplexing processing, video elementary stream (ES), audioES, and optionally subtitle are generated. The video decoder 3206, whichincludes the video decoder 30 as explained in the above-mentionedembodiments, decodes the video ES by the decoding method as shown in theabove-mentioned embodiments to generate video frame, and feeds this datato the synchronous unit 3212. The audio decoder 3208, decodes the audioES to generate audio frame, and feeds this data to the synchronous unit3212. Alternatively, the video frame may store in a buffer (not shown inFIG. 7) before feeding it to the synchronous unit 3212. Similarly, theaudio frame may store in a buffer (not shown in FIG. 7) before feedingit to the synchronous unit 3212.

The synchronous unit 3212 synchronizes the video frame and the audioframe, and supplies the video/audio to a video/audio display 3214. Forexample, the synchronous unit 3212 synchronizes the presentation of thevideo and audio information. Information may code in the syntax usingtime stamps concerning the presentation of coded audio and visual dataand time stamps concerning the delivery of the data stream itself.

If subtitle is included in the stream, the subtitle decoder 3210 decodesthe subtitle, synchronizes it with the video frame and the audio frame,and supplies the video/audio/subtitle to a video/audio/subtitle display3216.

The present disclosure is not limited to the above-mentioned system, andeither the picture encoding device or the picture decoding device in theabove-mentioned embodiments can be incorporated into other system, forexample, a car system.

Furthermore, FIG. 8 illustrates a flowchart of a method for inversequantization of a current block of a picture, the method being performedby a decoder, according to an embodiment of the present disclosure. InFIG. 8, a method for inverse quantization of a current block of apicture, wherein the method is performed by a decoder, is shown toinclude the operations:

Operations: (1601) receiving a bitstream; (1603) obtaining a jointchrominance component residual, JCCR, control flag from the bitstream;(1605) obtaining a chrominance mapping information from the bitstreambased on the JCCR control flag; (1607) obtaining at least onechrominance quantization parameter, QP, offset from the bitstream basedon the JCCR control flag; (1609) obtaining a QP value for the currentchrominance block based on the obtained chrominance mapping informationand the at least one obtained chrominance QP offset; and (1611)performing inverse quantization on the current chrominance block byusing the determined QP value.

In addition, FIG. 9 illustrates a flowchart of a method for inversequantization of a current block of a picture, the method being performedby a decoder, according to a further embodiment of the presentdisclosure. In FIG. 9, a method for inverse quantization of a currentblock of a picture, wherein the method is performed by a decoder, andthe method is shown to include the following operations: (1651)receiving a bitstream, wherein the bitstream comprises a Slice Headersyntax and a PPS syntax; (1653) obtaining syntax elements from the PPSsyntax, wherein the obtained syntax elements comprise chrominancequantization parameter, QP, offsets; (1655) obtaining chrominance QPoffset information from the Slice Header, wherein the QP offsetinformation is obtained independently of any PPS syntax elements in thePPS syntax; (1657) determining a QP value for the current chrominanceblock depending on the chrominance QP offset obtained from the PPSsyntax and the chrominance QP offset information obtained from the SliceHeader syntax; and (1659) performing inverse quantization on the currentchrominance block by using the determined QP value.

Moreover, FIG. 10 illustrates a flowchart of a method for inversequantization of a current block of a picture, the method being performedby an encoder, according to an embodiment of the present disclosure. InFIG. 10, a method for inverse quantization of a current block of apicture, wherein the method is performed by an encoder, is shown toinclude the following operations: (2601) encoding a joint chrominancecomponent residual, JCCR, control flag into a bitstream; (2603) encodinga chrominance mapping information into the bitstream based on the JCCRcontrol flag; (2605) encoding at least one chrominance quantizationparameter, QP, offset into the bitstream based on the JCCR control flag;and (2607) providing the bitstream.

Moreover, FIG. 11 illustrates a flowchart of a method for inversequantization of a current block of a picture, the method being performedby an encoder, according to the present disclosure. In FIG. 11, a methodfor inverse quantization of a current block of a picture, wherein themethod is performed by an encoder, is shown to include the followingoperations:

Operations: (2651) encoding syntax elements from Slice Header and PPSsyntax into a bitstream, wherein the syntax elements comprisechrominance quantization parameter, QP, offsets; (2653) encodingchrominance QP offset information from the Slice Header into thebitstream, wherein the QP offset information is obtained independentlyof any PPS syntax elements in the PPS syntax; and (2655) providing thebitstream.

Furthermore, FIG. 12 illustrates a decoder 30 according to an embodimentof the present disclosure. The decoder 30 of FIG. 12 comprises: areceiving unit 3001 configured to receive a bitstream; a first obtainingunit 3003 configured to obtain a joint chrominance component residual,JCCR, control flag from the bitstream; a second obtaining unit 3005configured to obtain a chrominance mapping information from thebitstream based on the JCCR control flag; a third obtaining unit 3007configured to obtain at least one chrominance quantization parameter,QP, offset from the bitstream based on the JCCR control flag; a fourthobtaining unit 3009 configured to obtain a QP value for the currentchrominance block based on the obtained chrominance mapping informationand the at least one obtained chrominance QP offset; and an inversequantizing unit (3011) configured to perform inverse quantization on thecurrent chrominance block by using the determined QP value.

Furthermore, FIG. 13 illustrates a decoder 30 according to anotherembodiment of the present disclosure. The decoder 30 of FIG. 13comprises: a receiving unit 3051 configured to receive a bitstream,wherein the bitstream comprises a Slice Header syntax and a PPS syntax;a first obtaining unit 3053 configured to obtain syntax elements fromthe PPS syntax, wherein the obtained syntax elements compriseschrominance quantization parameter, QP, offsets; a second obtaining unit3055 configured to obtain chrominance QP offset information from theSlice Header, wherein the QP offset information is obtainedindependently of any PPS syntax elements in the PPS syntax; adetermining unit 3057 configured to determining a QP value for thecurrent chrominance block depending on the chrominance QP offsetobtained from the PPS syntax and the chrominance QP offset informationobtained from the Slice Header syntax; and an inverse quantization unit3059 configured to perform inverse quantization on the currentchrominance block by using the determined QP value.

Furthermore, FIG. 14 illustrates an encoder 20 according to anembodiment of the present disclosure. The encoder 20 of FIG. 14comprises: a first encoding unit 2001 configured to encode a jointchrominance component residual, JCCR, control flag into a bitstream; asecond encoding unit 2003 configured to encode a chrominance mappinginformation into the bitstream based on the JCCR control flag; a thirdencoding unit 2005 configured to encode at least one chrominancequantization parameter, QP, offset into the bitstream based on the JCCRcontrol flag; and a providing unit 2007 configured to provide thebitstream.

Furthermore, FIG. 15 illustrates an encoder 20 according to anotherembodiment of the present disclosure. The encoder 20 of FIG. 15comprises: a first encoding unit 2051 configured to encode syntaxelements from Slice Header and PPS syntax into a bitstream, wherein thesyntax elements comprise chrominance quantization parameter, QP,offsets;

a second encoding unit 2053 configured to encode chrominance QP offsetinformation from the Slice Header into the bitstream, wherein the QPoffset information is obtained independently of any PPS syntax elementsin the PPS syntax; and a providing unit 2055 configured to provide thebitstream.

Mathematical Operators

The mathematical operators used in this application are similar to thoseused in the C programming language. However, the results of integerdivision and arithmetic shift operations are defined more precisely, andadditional operations are defined, such as exponentiation andreal-valued division. Numbering and counting conventions generally beginfrom 0, e.g., “the first” is equivalent to the 0-th, “the second” isequivalent to the 1-th, etc.

Arithmetic Operators

The following arithmetic operators are defined as follows:

-   -   + Addition    -   − Subtraction (as a two-argument operator) or negation (as a        unary prefix operator)    -   * Multiplication, including matrix multiplication    -   x^(y) Exponentiation. Specifies x to the power of y. In other        contexts, such notation is used for superscripting not intended        for interpretation as exponentiation.    -   / Integer division with truncation of the result toward zero.        For example, 7/4 and −7/−4 are truncated to 1 and −7/4 and 7/−4        are truncated to −1.    -   ÷ Used to denote division in mathematical equations where no        truncation or rounding is intended.

$\frac{x}{y}$

-   -   Used to denote division in mathematical equations where no        truncation or rounding is intended.

$\sum\limits_{i = x}^{y}{f(i)}$

-   -   The summation of f(i) with i taking all integer values from x up        to and including y.    -   x % y Modulus. Remainder of x divided by y, defined only for        integers x and y with x>=0 and y>0.

Logical Operators

The following logical operators are defined as follows:

-   -   x && y Boolean logical “and” of x and y    -   x∥y Boolean logical “or” of x and y    -   ! Boolean logical “not”    -   x ? y:z If x is TRUE or not equal to 0, evaluates to the value        of y; otherwise, evaluates to the value of z.

Relational Operators

The following relational operators are defined as follows:

-   -   > Greater than    -   >= Greater than or equal to    -   < Less than    -   <= Less than or equal to    -   == Equal to    -   != Not equal to

When a relational operator is applied to a syntax element or variablethat has been assigned the value “na” (not applicable), the value “na”is treated as a distinct value for the syntax element or variable. Thevalue “na” is considered not to be equal to any other value.

Bit-Wise Operators

The following bit-wise operators are defined as follows:

-   -   & Bit-wise “and”. When operating on integer arguments, operates        on a two's complement representation of the integer value. When        operating on a binary argument that contains fewer bits than        another argument, the shorter argument is extended by adding        more significant bits equal to 0.    -   | Bit-wise “or”. When operating on integer arguments, operates        on a two's complement representation of the integer value. When        operating on a binary argument that contains fewer bits than        another argument, the shorter argument is extended by adding        more significant bits equal to 0.    -   {circumflex over ( )} A Bit-wise “exclusive or”. When operating        on integer arguments, operates on a two's complement        representation of the integer value. When operating on a binary        argument that contains fewer bits than another argument, the        shorter argument is extended by adding more significant bits        equal to 0.    -   x>>y Arithmetic right shift of a two's complement integer        representation of x by y binary digits. This function is defined        only for non-negative integer values of y. Bits shifted into the        most significant bits (MSBs) as a result of the right shift have        a value equal to the MSB of x prior to the shift operation.    -   x<<y Arithmetic left shift of a two's complement integer        representation of x by y binary digits. This function is defined        only for non-negative integer values of y. Bits shifted into the        least significant bits (LSBs) as a result of the left shift have        a value equal to 0.

Assignment Operators

The following arithmetic operators are defined as follows:

-   -   = Assignment operator    -   ++ Increment, i.e., x++ is equivalent to x=x+1; when used in an        array index, evaluates to the value of the variable prior to the        increment operation.    -   −− Decrement, i.e., x−− is equivalent to x=x−1; when used in an        array index, evaluates to the value of the variable prior to the        decrement operation.    -   += Increment by amount specified, i.e., x+=3 is equivalent to        x=x+3, and x+=(−3) is equivalent to x=x+(−3).    -   −= Decrement by amount specified, i.e., x−=3 is equivalent to        x=x−3, and x−=(−3) is equivalent to x=x−(−3).

Range Notation

The following notation is used to specify a range of values:

-   -   x=y . . . z x takes on integer values starting from y to z,        inclusive, with x, y, and z being integer numbers and z being        greater than y.

Mathematical Functions

The following mathematical functions are defined:

${{Abs}(x)} = \left\{ \begin{matrix}{x;} & {x>=0} \\{{- x};} & {x < 0}\end{matrix} \right.$

-   -   A sin(x) the trigonometric inverse sine function, operating on        an argument x that is in the range of −1.0 to 1.0, inclusive,        with an output value in the range of −π+2 to π+2, inclusive, in        units of radians    -   A tan(x) the trigonometric inverse tangent function, operating        on an argument x, with an output value in the range of −π+2 to        π+2, inclusive, in units of radians

${A\tan 2\left( {y,x} \right)} = \left\{ \begin{matrix}{{A\;{\tan\ \left( \frac{y}{x} \right)}};} & {\ {x > 0}} \\{{{A\;{\tan\ \left( \frac{y}{x} \right)}} + \pi};} & {\ {{{{{{x < 0}\ \&}\&}\ y} >} = 0}} \\{{{A\;{\tan\ \left( \frac{y}{x} \right)}} - \pi};} & {\ {{{{{x < 0}\ \&}\&}\ y} < 0}} \\{{+ \frac{\pi}{2}};} & {\ {{{x==0}\ \&\&\ {y >}} = 0}} \\{{- \frac{\pi}{2}};} & {\ {otherwise}}\end{matrix} \right.$

-   -   Ceil(x) the smallest integer greater than or equal to x.

Clip1_(Y)(x)=Clip3(0,(1<<BitDepth_(Y))−1,x)

Clip1_(C)(x)=Clip3(0,(1<<BitDepth_(C))−1,x)

${Clip3\left( {x,y,z} \right)} = \left\{ \begin{matrix}{x;} & {\ {z < x}} \\{y;} & {z > y} \\{z;} & {otherwise}\end{matrix} \right.$

-   -   Cos(x) the trigonometric cosine function operating on an        argument x in units of radians    -   Floor(x) the largest integer less than or equal to x.

${{GetCurrMsb}\left( {a,b,c,d} \right)} = \left\{ \begin{matrix}{{c + d};} & {\ {{b - a}\ >={d/2}}} \\{{c - d};} & {\ {{a - b}\  > {d/2}}} \\{c;} & {otherwise}\end{matrix} \right.$

-   -   Ln(x) the natural logarithm of x (the base-e logarithm, where e        is the natural logarithm base constant 2.718 281 828 . . . ).    -   Log 2(x) the base-2 logarithm of x.    -   Log 10(x) the base-10 logarithm of x.

${{Min}\left( {x,y} \right)} = \left\{ {{\begin{matrix}{x;} & {x<=y} \\{y;} & {x > y}\end{matrix}{{Max}\left( {x,y} \right)}} = \left\{ \begin{matrix}{x;} & {x>=y} \\{y;} & {x < y}\end{matrix} \right.} \right.$Round(x)=Sign(x)*Floor(Abs(x)+0.5)

${{Sign}(x)} = \left\{ \begin{matrix}{1;} & {\ {x > 0}} \\{0;} & {\ {x==0}} \\{{- 1};} & {\ {x < 0}}\end{matrix} \right.$

Sin(x) the trigonometric sine function operating on an argument x inunits of radians

Sqrt(x)=√{square root over (x)}

Swap(x,y)=(y,x)

-   -   Tan(x) the trigonometric tangent function operating on an        argument x in units of radians

Order of Operation Precedence

When an order of precedence in an expression is not indicated explicitlyby use of parentheses, the following rules apply:

-   -   Operations of a higher precedence are evaluated before any        operation of a lower precedence.    -   Operations of the same precedence are evaluated sequentially        from left to right.

The table below specifies the precedence of operations from highest tolowest; a higher position in the table indicates a higher precedence.

For those operators that are also used in the C programming language,the order of precedence used in this Specification is the same as usedin the C programming language.

TABLE Operation precedence from highest (at top of table) to lowest (atbottom of table) operations (with operands x, y, and z) ″x++″, ″x−−″″!x″, ″−x″(as a unary prefix operator) x^(y) ″x * y″, ″x/y″, ″x ÷ y″, ″x/y″, ″x % y″ ″x + y″, ″x − y″ (as a two-argument operator),${''}{\sum\limits_{i = x}^{y}\;{{f(i)}{''}}}$ ″x << y″, ″x >> y″ ″x <y″, ″x <= y″, ″x > y″, ″x >= y″ ″x ==y″, ″x != y″ ″x & y″ ″x | y″ ″x &&y″ ″x ∥ y″ ″x ? y:z″ ″x . . . y″ ″x = y″, ″x +=y″, ″x −= y″

Text Description of Logical Operations

In the text, a statement of logical operations as would be describedmathematically in the following form:

if( condition 0 )  statement 0 else if( condition 1 )  statement 1 ...else /* informative remark on remaining condition */  statement n   maybe described in the following manner: ... as follows / ... the followingapplies:    If condition 0, statement 0    Otherwise, if condition 1,statement 1    ...    Otherwise (informative remark on remainingcondition), statement n

Each “If . . . Otherwise, if . . . Otherwise, . . . ” statement in thetext is introduced with “ . . . as follows” or “ . . . the followingapplies” immediately followed by “If . . . ”. The last condition of the“If . . . Otherwise, if . . . Otherwise, . . . ” is always an“Otherwise, . . . ”. Interleaved “If . . . Otherwise, if . . .Otherwise, . . . ” statements can be identified by matching “ . . . asfollows” or “ . . . the following applies” with the ending “Otherwise, .. . ”.

In the text, a statement of logical operations as would be describedmathematically in the following form:

if( condition 0a && condition 0b )  statement 0 else if( condition 1a || condition 1b )  statement 1 ... else  statement n  may be described inthe following manner: ... as follows / ... the following applies:   Ifall of the following conditions are true, statement 0:    condition 0a   condition 0b   Otherwise, if one or more of the following conditionsare true, statement 1:    condition 1a    condition 1b   ...  Otherwise, statement n

In the text, a statement of logical operations as would be describedmathematically in the following form:

if( condition 0 )  statement 0 if( condition 1 )  statement 1   may bedescribed in the following manner: When condition 0, statement 0 Whencondition 1, statement 1

Although embodiments of the disclosure have been primarily describedbased on video coding, it should be noted that embodiments of the codingsystem 10, encoder 20 and decoder 30 (and correspondingly the system 10)and the other embodiments described herein may also be configured forstill picture processing or coding, i.e. the processing or coding of anindividual picture independent of any preceding or consecutive pictureas in video coding. In general, only inter-prediction units 244(encoder) and 344 (decoder) may not be available in case the pictureprocessing coding is limited to a single picture 17. All otherfunctionalities (also referred to as tools or technologies) of the videoencoder 20 and video decoder 30 may equally be used for still pictureprocessing, e.g. residual calculation 204/304, transform 206,quantization 208, inverse quantization 210/310, (inverse) transform212/312, partitioning 262/362, intra-prediction 254/354, and/or loopfiltering 220, 320, and entropy coding 270 and entropy decoding 304.

Embodiments, e.g. of the encoder 20 and the decoder 30, and functionsdescribed herein, e.g. with reference to the encoder 20 and the decoder30, may be implemented in hardware, software, firmware, or anycombination thereof. If implemented in software, the functions may bestored on a computer-readable medium or transmitted over communicationmedia as one or more instructions or code and executed by ahardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media, which is non-transitory, or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limiting, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. In addition, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. In addition, thetechniques could be fully implemented in one or more circuits or logicelements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

The present disclosure provides the following nineteen further aspects:

A first aspect of a method for inverse quantization of a current blockof a picture, wherein the method is performed by a decoder, and themethod comprising:

receiving a bitstream, wherein the bitstream comprises a Slice Headersyntax and a PPS syntax;

obtaining syntax elements from the PPS syntax, wherein the obtainedsyntax elements comprises chrominance quantization parameter (QP)offsets;

obtaining chrominance QP offset information from the Slice Header,wherein the QP offset information is obtained independently of any PPSsyntax elements in the PPS syntax;

determining a QP value for the current chrominance block depending onthe chrominance QP offsets obtained from the PPS syntax and thechrominance QP offset information obtained from the Slice Header syntax;

performing inverse quantization on the current chrominance block byusing the determined QP value.

A second aspect of a method according to the first aspect, wherein theat least one chrominance QP offset obtained from the PPS syntaxcomprises: pps_cb_qp_offset, pps_cr_qp_offset, pps_joint_cbcr_qp_offset,and cu_chroma_qp_offset_enabled_flag.

A third aspect of a method according to the second aspect, wherein ifthe value of the cu_chroma_qp_offset_enabled_flag is true (e.g., thevalue of the cu_chroma_qp_offset_enabled_flag is 1), the chrominance QPoffsets obtained from the PPS syntax further comprises:cu_chroma_qp_offset_subdiv, chroma_qp_offset_list_len_minus1,cb_qp_offset_list[i], cr_qp_offset_list[i] andjoint_cbcr_qp_offset_list[i], wherein0≤i≤chroma_qp_offset_list_len_minus1 and i is a integer.

A fourth aspect of a method according to any one of the first to thirdaspects, wherein the chrominance QP offset information obtained from theSlice Header syntax comprises: slice_cb_qp_offset andslice_cr_qp_offset.

A fifth aspect of a method according to the fourth aspect, wherein ifthe value of a sps_joint_cbcr_enabled_flag (e.g., an element of an SPSlevel syntax comprised in the bitstream) is true (e.g., the value of thesps_joint_cbcr_enabled_flag is 1), the chrominance QP offset informationobtained from the Slice Header syntax further comprises:slice_joint_cbcr_qp_offset.

A sixth aspect of a method according to any one of the first to fifthaspects, wherein the PPS syntax comprises the following structure:

pic_parameter_set_rbsp( ) { Descriptor ...  pps_cb_qp_offset se(v) pps_cr_qp_offset se(v)  pps_joint_cbcr_qp_offset se(v) cu_chroma_qp_offset_enabled_flag u(1)  if( cu_chroma_qp_offset_ enabled_flag ) {   cu_chroma_qp_offset_subdiv ue(v)  chroma_qp_offset_list_len_minus1 ue(v)   for( i = 0; i <=chroma_qp_offset_   list_len_minus1; i++ ) {    cb_qp_offset_list[ i ]se(v)    cr_qp_offset_list[ i ] se(v)    joint_cbcr_qp_offset_list[ i ]se(v)   }  } ... }

A seventh aspect of a method according to any one of the first to sixthaspects, wherein the slice header syntax comprises the followingstructure:

slice_header( ) { Descriptor ...  slice_cb_qp_offset se(v) slice_cr_qp_offset se(v)  if( sps_joint_cbcr_enabled_flag )  slice_joint_cbcr_qp_offset se(v) ... }

An eighth aspect of a method according to any one of the first toseventh aspects, wherein the flagpps_slice_chroma_qp_offsets_present_flag is omitted in the PPS syntax;or

wherein the Slice Header and the PPS syntax always comprise elementsrelated to chrominance QP offset.

A ninth aspect of a method for inverse quantization of a current blockof a picture, wherein the method is performed by a decoder, and themethod comprising:

receiving a bitstream;

obtaining a joint chrominance component residual (JCCR) control flagfrom the bitstream;

obtaining a chrominance mapping information from the bitstream based onthe JCCR control flag;

obtaining chrominance quantization parameter (QP) offsets from thebitstream based on the JCCR control flag;

obtaining a QP value for the current chrominance block based on theobtained chrominance mapping information and the obtained chrominance QPoffsets;

performing inverse quantization on the current chrominance block byusing the determined QP value.

A tenth aspect of a method according to the ninth aspect, wherein thebitstream comprises a SPS level syntax, and the JCCR control flag isobtained from the SPS level syntax.

An eleventh aspect of a method according to the ninth or tenth aspect,wherein the JCCR control flag is sps_joint_cbcr_enabled_flag.

A twelfth aspect of a method according to any one of the ninth toeleventh aspect, wherein the chrominance mapping information comprisesdelta_qp_in_val_minus1[i][j] and delta_qp_out_val[i][j], and thechrominance mapping information is obtained from a SPS level syntaxcomprised by the bitstream.

A thirteenth aspect of a method according to any one of the ninth totwelfth aspect, wherein the SPS level syntax comprises the followingstructure:

seq_parameter_set_rbsp( ) { Descriptor ...  if( ChromaArrayType != 0 ) {  same_qp_table_for_chroma u(1)   for( i = 0; i <same_qp_table_for_chroma ?   1 : sps_joint_cbcr_enabled_flag ? 3 : 2;i++ ) {    num_points_in_qp_table_minus1[ i ] ue(v)    for( j = 0; j <=num_points_in_qp_    table_minus1[ i ]; j++ ) {    delta_qp_in_val_minus1[ i ][ j ] ue(v)     delta_qp_out_val[ i ][ j] ue(v)    }   }  } ... }

A fourteenth aspect of a method according to any one of the ninth tothirteenth aspect, wherein the obtaining chrominance QP offsets from thebitstream based on the JCCR control flag comprises:

obtaining, based on the JCCR control flag, the chrominance QP offsetsfrom a PPS level syntax of the bitstream.

A fifteenth aspect of a method according to the fourteenth aspect,wherein the PPS level syntax comprises the following structure:

pic_parameter_set_rbsp( ) { Descriptor ...  pps_cb_qp_offset se(v) pps_cr_qp_offset se(v)  if( sps_joint_cbcr_enabled_flag )  pps_joint_cbcr_qp_offset se(v)  cu_chroma_qp_offset_enabled_flag u(1) if( cu_chroma_qp_offset_enabled_flag ) {   cu_chroma_qp_offset_subdivue(v)   chroma_qp_offset_list_len_minus1 ue(v)   for( i = 0; i <=chroma_qp_offset_   list_minus1; i++ ) {    cb_qp_offset_list[ i ] se(v)   cr_qp_offset_list[ i ] se(v)    if( sps_joint_cbcr_enabled_flag )    joint_cbcr_qp_offset_list[ i ] se(v)   }  } ... }

A sixteenth aspect of a decoder comprising processing circuitry forcarrying out the method according to any one of the first to fifteenthaspect.

A seventeenth aspect of a computer program product comprising programcode for performing the method according to any one of the precedingaspects when executed on a computer or a processor.

An eighteenth aspect of a decoder, comprising:

one or more processors; and

a non-transitory computer-readable storage medium coupled to theprocessors and storing programming for execution by the processors,wherein the programming, when executed by the processors, configures thedecoder to carry out the method according to any one of the precedingaspects.

A nineteenth aspect of a non-transitory computer-readable mediumcarrying a program code which, when executed by a computer device,causes the computer device to perform the method of any one of thepreceding aspects.

What is claimed is:
 1. A method for inverse quantization of a currentblock of a picture, wherein the method is performed by a decoder, andthe method comprising: receiving a bitstream; obtaining a jointchrominance component residual (JCCR) control flag from the bitstream;obtaining a chrominance mapping information from the bitstream based onthe JCCR control flag; obtaining at least one chrominance quantizationparameter (QP) offset from the bitstream based on the JCCR control flag;obtaining a QP value for the current chrominance block based on theobtained chrominance mapping information and the at least one obtainedchrominance QP offset; and performing inverse quantization on thecurrent chrominance block by using the obtained QP value.
 2. The methodaccording to claim 1, wherein the bitstream comprises a sequenceparameter set (SPS) level syntax, and the JCCR control flag is obtainedfrom the SPS level syntax.
 3. The method according to claim 1, whereinthe JCCR control flag is the sps_joint_cbcr_enabled_flag.
 4. The methodaccording to claim 3, wherein if a value of thesps_joint_cbcr_enabled_flag is 1, the at least one obtained chrominanceQP offset is specified by slice_joint_cbcr_qp_offset.
 5. The methodaccording to claim 1, wherein the chrominance mapping informationcomprises delta_qp_in_val_minus1[i][j] and delta_qp_out_val[i][j], andthe chrominance mapping information is obtained from an SPS level syntaxcomprised in the bitstream.
 6. The method according to claim 1, whereinthe obtaining the at least one chrominance QP offset from the bitstreambased on the JCCR control flag comprises: obtaining, based on the JCCRcontrol flag, the at least one chrominance QP offset from a pictureparameter set (PPS) level syntax of the bitstream.
 7. A method forencoding a current block of a picture, wherein the method is performedby an encoder, the method comprising: encoding a joint chrominancecomponent residual (JCCR) control flag into a bitstream; encoding achrominance mapping information into the bitstream based on the JCCRcontrol flag; encoding at least one chrominance quantization parameter(QP) offset into the bitstream based on the JCCR control flag; providingthe bitstream.
 8. The method according to claim 7, wherein the bitstreamcomprises a sequence parameter set (SPS) level syntax, and the JCCRcontrol flag is encoded into the SPS level syntax.
 9. The methodaccording to claim 7, wherein the JCCR control flag is thesps_joint_cbcr_enabled_flag.
 10. The method according to claim 9,wherein if a value of the sps_joint_cbcr_enabled_flag is 1, the at leastone encoded chrominance QP offset is specified byslice_joint_cbcr_qp_offset.
 11. The method according to claim 7, whereinthe chrominance mapping information comprisesdelta_qp_in_val_minus1[i][j] and delta_qp_out_val[i][j], and thechrominance mapping information is encoded into an SPS level syntaxcomprised in the bitstream.
 12. The method according to claim 7, whereinthe encoding the at least one chrominance QP offset into the bitstreambased on the JCCR control flag comprises: encoding, based on the JCCRcontrol flag, the at least one chrominance QP offset into a pictureparameter set (PPS) level syntax of the bitstream.
 13. A video decodingdevice, comprising: a non-transitory memory storage, configured to storevideo data in a form of a bitstream; and a video decoder, configured to:receive the bitstream; obtain a joint chrominance component residual(JCCR) control flag from the bitstream; obtain a chrominance mappinginformation from the bitstream based on the JCCR control flag; obtain atleast one chrominance quantization parameter (QP) offset from thebitstream based on the JCCR control flag; obtain a QP value for acurrent chrominance block based on the obtained chrominance mappinginformation and the at least one obtained chrominance QP offset; andperforming inverse quantization on the current chrominance block byusing the determined QP value.
 14. The video decoding device accordingto claim 13, wherein the bitstream comprises a sequence parameter set(SPS) level syntax, and the JCCR control flag is obtained from the SPSlevel syntax.
 15. The video decoding device according to claim 13,wherein the JCCR control flag is the sps_joint_cbcr_enabled_flag. 16.The video decoding device according to claim 15, wherein if a value ofthe sps_joint_cbcr_enabled_flag is 1, the at least one obtainedchrominance QP offset is specified by slice_joint_cbcr_qp_offset. 17.The video decoding device according to claim 13, wherein the chrominancemapping information comprises delta_qp_in_val_minus1[i][j] anddelta_qp_out_val[i][j], and the chrominance mapping information isobtained from an SPS level syntax comprised in the bitstream.
 18. Thevideo decoding device according to claim 13, wherein the video decodingdevice is further configured to: obtaining, based on the JCCR controlflag, the at least one chrominance QP offset from a picture parameterset (PPS) level syntax of the bitstream.